BASIC ANATOMY OF THE HUMAN
HEART
In the venous pole, blood enters via the caval veins (superior & inferior vena cava) and
coronary sinus into the right atrium (RA). From the RA, blood passes through the
tricuspid valve into the right ventricle (RV). The RV pumps blood through the
pulmonary valve into the pulmonary trunk toward the lungs. Oxygenated blood
returns via the pulmonary veins into the left atrium (LA). From the LA, blood flows
through the mitral valve into the left ventricle (LV). The LV pumps it through the aortic
valve into the aorta for systemic circulation. The stepwise sequence of valves and
chambers:
• Venous inflow (caval veins/pulmonary veins).
• Atria → AV valves.
• Ventricles → VA (ventriculo-arterial) valves.
• Outflow tracts (pulmonary trunk/aorta).
Topography of the heart
The ventral view of the heart shows the four main chambers (RA, RV, LA, LV). The superior caval vein is the
large vein entering the right atrium from above. Both the aorta and pulmonary trunk appear at the superior
part of the heart (always positioned at the top in ventral views). The interventricular sulcus is the groove
marking the boundary between the right and left ventricles. Base of the heart is the superior, broad part
where major vessels exit. The inferior, pointed tip directed left and downward is the apex of the heart. The
pericardial reflection (cut edge) is part of the pericardium surrounding the heart. How to orient the heart
in situ:
• The apex points left and down.
• The base with great vessels sits superiorly.
• The sulci help distinguish external chamber boundaries.
Apex focus emphasizes the apex of the heart, which is formed almost entirely by the left ventricle. The
apex points downward, forward, and left, resting on the diaphragm.
The dorsal view (back) of the heart shows the LA prominently, since it lies posteriorly. The pulmonary veins
enter the LA from the back. The inferior vena cava (IVC) is visible at the inferior aspect, draining into the
RA. The coronary sinus is also seen posteriorly, delivering venous blood from the myocardium into the RA.
The caudal view (bottom) of the heart shows a view looking upward from beneath the heart. It highlights
the IVC, always positioned at the lowest point entering the RA. The LV and RV inferior walls are also visible.
The apex points leftward.
Ventral view Dorsal view Caudal view
, The heart is located inside the pericardial sac, which consists of:
• Visceral sheet (visceral pericardium = epicardium): directly on the heart.
• Parietal sheet (parietal pericardium): outer layer.
• Cavity between them = pericardial cavity, filled with fluid.
The pericardial cavity developing from the pericardio-peritoneal canals,
which later give rise to the pleural cavities. The pleuro-pericardial
membrane will separate the pleural cavity (lungs) from the pericardial
cavity (heart). The pleuro-peritoneal membrane contributes to the
primordial diaphragm (blue). The pleuro-pericardial membrane develops into the fibrous pericardium
(yellow). The pleuro-peritoneal membrane becomes part of the diaphragm. The final adult pericardial:
• Fibrous pericardium (outermost, continuous with the central tendon of diaphragm, innervated by
phrenic nerve).
• Parietal pericardium (inner lining of fibrous pericardium).
• Visceral pericardium (epicardium) on the heart.
• Pericardial cavity in between (contains lubricating fluid).
Morphology of the compartments
Key features of the right atrium (RA):
• Large, broad auricle
o The auricle (atrium’s appendage) on the right is wide and muscular.
• Terminal crest (crista terminalis)
o A ridge inside the RA separating two zones:
▪ Smooth-walled sinus venarum (where venae cavae and coronary sinus open).
▪ Rough, muscular pectinate part (auricle).
• Oval fossa (fossa ovalis)
o Depression in the interatrial septum, remnant of the foramen ovale (fetal circulation).
o Surrounded by the limbus of the oval fossa (formed by the secondary septum).
• Membranous septum (AV part)
o Thin part of the septum near
the atrioventricular junction.
• Eustachian valve (of the IVC)
o Small ridge at the opening of
the inferior vena cava.
o In the fetus, helps direct blood
toward the foramen ovale.
• Thebesian valve
o Guards the entrance of the
coronary sinus into the RA.
• Tricuspid valve
, o RA communicates with the right ventricle through this AV valve.
Key features of the left atrium (LA):
• Small, narrow auricle
o The appendage is smaller and more
tubular than the broad right auricle.
• Pulmonary veins
o The LA receives oxygenated blood from
the lungs through usually four pulmonary
veins (two right, two left).
o These openings are smooth-walled and
directly enter the chamber.
• Valve of the oval foramen (remnant of primary atrial septum)
o Located in the interatrial septum, this acts as the valve to the foramen ovale during fetal
life.
• Limbus of the oval fossa (from the secondary atrial septum)
o The raised ridge that frames the fossa, seen on both atrial sides.
Right Atrium (RA) Left Atrium (LA)
Large broad auricle (pectinate muscles) Small, narrow auricle
Venous inflow: SVC, IVC, coronary sinus Venous inflow: pulmonary veins
Fossa ovalis floor = primary septum Fossa ovalis valve = primary septum
More visible embryological remnants (Eustachian
Cleaner, smoother walls, fewer valves
& Thebesian valves)
Dominates systemic venous return Dominates pulmonary venous return
Key features of the right ventricle (RV):
• Pulmonary infundibulum (conus arteriosus)
• Smooth outflow tract leading to the
pulmonary valve.
• Tricuspid valve
• AV connection with RA, supported by
chordae tendineae and papillary muscles.
• Papillary muscles & tendinous cords
• Some cords attach directly to the septal
wall, unlike the LV (where they attach
only to the mural wall).
• Septomarginal trabeculation (moderator band)
• Muscular band crossing the cavity, carrying part of the right bundle branch.
• Trabeculation
• Coarse, irregular compared with the LV.
• Supraventricular crest
• Muscular ridge separating the inflow and outflow tracts.
The RV lumen is flattened, crescent-shaped in cross-section. Blood flow is angulated because of the
separated inflow (tricuspid) and outflow (pulmonary infundibulum) regions.
Key features of the left ventricle (LV):
• Mitral valve
o Two leaflets, connected via chordae
tendineae to papillary muscles.
• Papillary muscles
o Attach only to the mural wall, not
septal wall (contrast with RV).
• Trabeculation
o Fine and regular, unlike the coarse RV.
• Fibrous continuity
o Between mitral and aortic valves — no muscular crest (unlike RV).
, • Membranous septum
o Thin portion of the interventricular and atrioventricular septum near the outflow tract.
• Coronary ostia
o Openings of the coronary arteries just above the aortic valve cusps.
LV lumen is cylindrical and circular in cross-section. Blood flow is parallel and streamlined (inflow from
mitral valve → outflow through aortic valve).
Right Ventricle (RV) Left Ventricle (LV)
Crescent-shaped lumen Cylindrical, circular lumen
Coarse trabeculae Fine trabeculae
Moderator band present No moderator band
Separate inflow (tricuspid) & outflow Inflow (mitral) and outflow (aortic) in fibrous
(infundibulum, supraventricular crest) continuity
Thinner walls Thicker walls
Pumps to low-pressure pulmonary circuit Pumps to high-pressure systemic circuit
The cardiac skeleton is a dense fibrous structure at the base of the heart. It provides anchoring for the
heart valves and electrical insulation between atria and ventricles. Membranous septum (IV and AV parts)
connects into the fibrous skeleton. The valves move between diastole and systole, but remain anchored by
the fibrous rings. The cardiac skeleton keeps valves structurally aligned and electrically separates atria from
ventricles (only the AV node/bundle crosses). The tricuspid valve is positioned slightly more apically than
the mitral valve. This offset creates the atrioventricular (AV) and interventricular (IV) parts of the
membranous septum. This offset is clinically significant, congenital malformations (e.g., Ebstein’s anomaly)
involve abnormal displacement of the tricuspid valve.
Conduction system of the heart
The main components:
• Sinoatrial (SA) node: pacemaker, in right atrium near SVC.
• Atrioventricular (AV) node: in interatrial septum near coronary sinus.
• AV bundle (bundle of His): the only electrical connection across the cardiac skeleton.
• Right & left bundle branches: descend along interventricular septum.
• Purkinje fibers: terminal branches into ventricular myocardium.
The central parts of the conduction system are the SA node, AV node, proximal AV bundle, and bundle
branches. These are the primary pacemaking and conduction hubs and are located close to the
membranous septum and valve annuli. The peripheral parts are the Purkinje fibers spreading through the
ventricular myocardium. They run within the trabeculae of the ventricles, ensuring rapid and synchronous
contraction. They are organized in atrial chamber myocardium → distal branches → Purkinje trabeculation.
Central parts Peripheral parts
There is a transition from primary myocardium (automaticity, slow conduction, weak contraction) to
chamber myocardium (low automaticity, rapid conduction, strong contraction). Conduction tissues (SA
node, AV node, His bundle) retain primary myocardium features. Contractile myocardium (ventricular
walls) adopts chamber characteristics.
HEART
In the venous pole, blood enters via the caval veins (superior & inferior vena cava) and
coronary sinus into the right atrium (RA). From the RA, blood passes through the
tricuspid valve into the right ventricle (RV). The RV pumps blood through the
pulmonary valve into the pulmonary trunk toward the lungs. Oxygenated blood
returns via the pulmonary veins into the left atrium (LA). From the LA, blood flows
through the mitral valve into the left ventricle (LV). The LV pumps it through the aortic
valve into the aorta for systemic circulation. The stepwise sequence of valves and
chambers:
• Venous inflow (caval veins/pulmonary veins).
• Atria → AV valves.
• Ventricles → VA (ventriculo-arterial) valves.
• Outflow tracts (pulmonary trunk/aorta).
Topography of the heart
The ventral view of the heart shows the four main chambers (RA, RV, LA, LV). The superior caval vein is the
large vein entering the right atrium from above. Both the aorta and pulmonary trunk appear at the superior
part of the heart (always positioned at the top in ventral views). The interventricular sulcus is the groove
marking the boundary between the right and left ventricles. Base of the heart is the superior, broad part
where major vessels exit. The inferior, pointed tip directed left and downward is the apex of the heart. The
pericardial reflection (cut edge) is part of the pericardium surrounding the heart. How to orient the heart
in situ:
• The apex points left and down.
• The base with great vessels sits superiorly.
• The sulci help distinguish external chamber boundaries.
Apex focus emphasizes the apex of the heart, which is formed almost entirely by the left ventricle. The
apex points downward, forward, and left, resting on the diaphragm.
The dorsal view (back) of the heart shows the LA prominently, since it lies posteriorly. The pulmonary veins
enter the LA from the back. The inferior vena cava (IVC) is visible at the inferior aspect, draining into the
RA. The coronary sinus is also seen posteriorly, delivering venous blood from the myocardium into the RA.
The caudal view (bottom) of the heart shows a view looking upward from beneath the heart. It highlights
the IVC, always positioned at the lowest point entering the RA. The LV and RV inferior walls are also visible.
The apex points leftward.
Ventral view Dorsal view Caudal view
, The heart is located inside the pericardial sac, which consists of:
• Visceral sheet (visceral pericardium = epicardium): directly on the heart.
• Parietal sheet (parietal pericardium): outer layer.
• Cavity between them = pericardial cavity, filled with fluid.
The pericardial cavity developing from the pericardio-peritoneal canals,
which later give rise to the pleural cavities. The pleuro-pericardial
membrane will separate the pleural cavity (lungs) from the pericardial
cavity (heart). The pleuro-peritoneal membrane contributes to the
primordial diaphragm (blue). The pleuro-pericardial membrane develops into the fibrous pericardium
(yellow). The pleuro-peritoneal membrane becomes part of the diaphragm. The final adult pericardial:
• Fibrous pericardium (outermost, continuous with the central tendon of diaphragm, innervated by
phrenic nerve).
• Parietal pericardium (inner lining of fibrous pericardium).
• Visceral pericardium (epicardium) on the heart.
• Pericardial cavity in between (contains lubricating fluid).
Morphology of the compartments
Key features of the right atrium (RA):
• Large, broad auricle
o The auricle (atrium’s appendage) on the right is wide and muscular.
• Terminal crest (crista terminalis)
o A ridge inside the RA separating two zones:
▪ Smooth-walled sinus venarum (where venae cavae and coronary sinus open).
▪ Rough, muscular pectinate part (auricle).
• Oval fossa (fossa ovalis)
o Depression in the interatrial septum, remnant of the foramen ovale (fetal circulation).
o Surrounded by the limbus of the oval fossa (formed by the secondary septum).
• Membranous septum (AV part)
o Thin part of the septum near
the atrioventricular junction.
• Eustachian valve (of the IVC)
o Small ridge at the opening of
the inferior vena cava.
o In the fetus, helps direct blood
toward the foramen ovale.
• Thebesian valve
o Guards the entrance of the
coronary sinus into the RA.
• Tricuspid valve
, o RA communicates with the right ventricle through this AV valve.
Key features of the left atrium (LA):
• Small, narrow auricle
o The appendage is smaller and more
tubular than the broad right auricle.
• Pulmonary veins
o The LA receives oxygenated blood from
the lungs through usually four pulmonary
veins (two right, two left).
o These openings are smooth-walled and
directly enter the chamber.
• Valve of the oval foramen (remnant of primary atrial septum)
o Located in the interatrial septum, this acts as the valve to the foramen ovale during fetal
life.
• Limbus of the oval fossa (from the secondary atrial septum)
o The raised ridge that frames the fossa, seen on both atrial sides.
Right Atrium (RA) Left Atrium (LA)
Large broad auricle (pectinate muscles) Small, narrow auricle
Venous inflow: SVC, IVC, coronary sinus Venous inflow: pulmonary veins
Fossa ovalis floor = primary septum Fossa ovalis valve = primary septum
More visible embryological remnants (Eustachian
Cleaner, smoother walls, fewer valves
& Thebesian valves)
Dominates systemic venous return Dominates pulmonary venous return
Key features of the right ventricle (RV):
• Pulmonary infundibulum (conus arteriosus)
• Smooth outflow tract leading to the
pulmonary valve.
• Tricuspid valve
• AV connection with RA, supported by
chordae tendineae and papillary muscles.
• Papillary muscles & tendinous cords
• Some cords attach directly to the septal
wall, unlike the LV (where they attach
only to the mural wall).
• Septomarginal trabeculation (moderator band)
• Muscular band crossing the cavity, carrying part of the right bundle branch.
• Trabeculation
• Coarse, irregular compared with the LV.
• Supraventricular crest
• Muscular ridge separating the inflow and outflow tracts.
The RV lumen is flattened, crescent-shaped in cross-section. Blood flow is angulated because of the
separated inflow (tricuspid) and outflow (pulmonary infundibulum) regions.
Key features of the left ventricle (LV):
• Mitral valve
o Two leaflets, connected via chordae
tendineae to papillary muscles.
• Papillary muscles
o Attach only to the mural wall, not
septal wall (contrast with RV).
• Trabeculation
o Fine and regular, unlike the coarse RV.
• Fibrous continuity
o Between mitral and aortic valves — no muscular crest (unlike RV).
, • Membranous septum
o Thin portion of the interventricular and atrioventricular septum near the outflow tract.
• Coronary ostia
o Openings of the coronary arteries just above the aortic valve cusps.
LV lumen is cylindrical and circular in cross-section. Blood flow is parallel and streamlined (inflow from
mitral valve → outflow through aortic valve).
Right Ventricle (RV) Left Ventricle (LV)
Crescent-shaped lumen Cylindrical, circular lumen
Coarse trabeculae Fine trabeculae
Moderator band present No moderator band
Separate inflow (tricuspid) & outflow Inflow (mitral) and outflow (aortic) in fibrous
(infundibulum, supraventricular crest) continuity
Thinner walls Thicker walls
Pumps to low-pressure pulmonary circuit Pumps to high-pressure systemic circuit
The cardiac skeleton is a dense fibrous structure at the base of the heart. It provides anchoring for the
heart valves and electrical insulation between atria and ventricles. Membranous septum (IV and AV parts)
connects into the fibrous skeleton. The valves move between diastole and systole, but remain anchored by
the fibrous rings. The cardiac skeleton keeps valves structurally aligned and electrically separates atria from
ventricles (only the AV node/bundle crosses). The tricuspid valve is positioned slightly more apically than
the mitral valve. This offset creates the atrioventricular (AV) and interventricular (IV) parts of the
membranous septum. This offset is clinically significant, congenital malformations (e.g., Ebstein’s anomaly)
involve abnormal displacement of the tricuspid valve.
Conduction system of the heart
The main components:
• Sinoatrial (SA) node: pacemaker, in right atrium near SVC.
• Atrioventricular (AV) node: in interatrial septum near coronary sinus.
• AV bundle (bundle of His): the only electrical connection across the cardiac skeleton.
• Right & left bundle branches: descend along interventricular septum.
• Purkinje fibers: terminal branches into ventricular myocardium.
The central parts of the conduction system are the SA node, AV node, proximal AV bundle, and bundle
branches. These are the primary pacemaking and conduction hubs and are located close to the
membranous septum and valve annuli. The peripheral parts are the Purkinje fibers spreading through the
ventricular myocardium. They run within the trabeculae of the ventricles, ensuring rapid and synchronous
contraction. They are organized in atrial chamber myocardium → distal branches → Purkinje trabeculation.
Central parts Peripheral parts
There is a transition from primary myocardium (automaticity, slow conduction, weak contraction) to
chamber myocardium (low automaticity, rapid conduction, strong contraction). Conduction tissues (SA
node, AV node, His bundle) retain primary myocardium features. Contractile myocardium (ventricular
walls) adopts chamber characteristics.
