First Aid USMLE Step 1: Cardiovascular
2026/2027 | Ultimate All-in-One Medical Exam
Preparation with Complete Strategies &
Workbook | Latest Edition
Truncus arteriosus gives rise to __________. - ANSWERS-Ascending aorta and
pulmonary trunk What is cardiac looping? - ANSWERS--Primary heart tube
loops to establish left-right polarity; begins in week 4 of gestation.
Defect in left-right dynein (involved in L/R asymmetry) can lead
to___________, as seen in Kartagener syndrome (primary ciliary dyskinesia). -
ANSWERS-Dextrocardia
What is a foramen/ostium? - ANSWERS-opening
What is a septum? - ANSWERS-wall
Septation of atria (7 Steps) - ANSWERS-1. Septum primum grows toward
endocardial cushions, narrowing foramen primum.
2. Foramen secundum forms in septum primum (foramen primum
disappears).
3. Septum secundum develops as foramen secundum maintains right-to-left
shunt.
4. Septum secundum expands and covers most of the foramen secundum.
The residual foramen is the foramen ovale.
5. Remaining portion of septum primum forms valve of foramen ovale.
6. (Not shown) Septum secundum and septum primum fuse to form the atrial
septum.
,7. (Not shown) Foramen ovale usually closes
soon after birth because of increased LA pressure.
Patent foramen ovale is caused by a failure of __________ and ___________ to
fuse after birth. What can this lead to? - ANSWERS--Caused by failure of
septum primum and septum secundum to fuse after birth; most are left
untreated.
-Can lead to paradoxical emboli (venous thromboemboli that enter systemic
arterial circulation), similar to those resulting from an ASD.
Septation of the ventricles (3 steps) - ANSWERS-1. Muscular ventricular
septum forms. Opening is called interventricular foramen.
2. Aorticopulmonary septum rotates and fuses with muscular ventricular
septum to form membranous interventricular septum, closing
interventricular foramen.
3. Growth of endocardial cushions separates atria from ventricles and
contributes to both atrial septation and membranous portion of the
interventricular septum.
What is the most common congenital cardinal anomaly? - ANSWERS-VSD
Most common location of VSD? - ANSWERS-The membranous septum
Bulbus cordis gives rise to __________. - ANSWERS-Smooth parts (outflow
tract) of left and right ventricles
Endocardial cushion gives rise to? - ANSWERS-Atrial septum ,membraneous
interventricular septum; AV & semilunar valves
,Primitive atrium gives rise to __________. - ANSWERS-Trabeculated
(muscular) portions of the left and right atria
Primitive ventricle gives rise to __________. - ANSWERS-Trabeculated
(muscular) portions of the left and right ventricles
Primitive pulmonary vein gives rise to __________. - ANSWERS-Smooth part
of the right atrium
Left horn of sinus venosus gives rise to __________. - ANSWERS-Coronary
sinus
Right horn of sinus venosus gives rise to __________. - ANSWERS-Smooth
part of the right atrium (sinus venarum)
Right common cardinal vein and right anterior cardinal vein gives rise to
__________. - ANSWERS-Superior vena cava (SVC)
When does the heart beat begin to beat spontaneously? - ANSWERS--4
weeks of development
-First functional organ in vertebrate embryos
Outflow tract formation - ANSWERS-Truncus arteriosus rotates; neural crest
and endocardial cell migrations cause truncal and bulbar ridges that spiral
and fuse to form aorticopulmonary septum to form ascending aorta and
pulmonary trunk.
What are the conotruncal abnormalities associated w/ failure of neural crest
cells to migrate? - ANSWERS-Transposition of the greta vessels
, Tetralogy of Fallot
Persistent truncus arteriosus
Aortic/pulmonary valves are derived from ____________. - ANSWERS-The
endocardial cushions of outflow tract.
Mitral/tricuspid valves are derived from __________. - ANSWERS-Fused
endocardial cushions of the AV canal.
Fetal erythropoiesis occurs in ___________? - ANSWERS--Yolk sac (3-8 weeks)
-Liver (6 weeks-birth)
-Spleen (10-28 weeks)
-Bone marrow (18 weeks to adult)
Hemoglobin development - ANSWERS--Embryonic globins: ζ and ε.
-Fetal hemoglobin (HbF) = α2γ2.
-Adult hemoglobin (HbA1) = α2β2.
-HbF has higher affinity for O2 due to less avid binding of 2,3-BPG, allowing
HbF to extract O2 from maternal hemoglobin (HbA1 and HbA2) across the
placenta.
Fetal circulation diagram - ANSWERS-
Blood in umbilical vein has a Po2 of _________ and is ________ saturated with
O2. - ANSWERS-≈ 30 mmHg, ≈ 80%
Umbilical arteries have _____ O2 saturation. - ANSWERS-Low
2026/2027 | Ultimate All-in-One Medical Exam
Preparation with Complete Strategies &
Workbook | Latest Edition
Truncus arteriosus gives rise to __________. - ANSWERS-Ascending aorta and
pulmonary trunk What is cardiac looping? - ANSWERS--Primary heart tube
loops to establish left-right polarity; begins in week 4 of gestation.
Defect in left-right dynein (involved in L/R asymmetry) can lead
to___________, as seen in Kartagener syndrome (primary ciliary dyskinesia). -
ANSWERS-Dextrocardia
What is a foramen/ostium? - ANSWERS-opening
What is a septum? - ANSWERS-wall
Septation of atria (7 Steps) - ANSWERS-1. Septum primum grows toward
endocardial cushions, narrowing foramen primum.
2. Foramen secundum forms in septum primum (foramen primum
disappears).
3. Septum secundum develops as foramen secundum maintains right-to-left
shunt.
4. Septum secundum expands and covers most of the foramen secundum.
The residual foramen is the foramen ovale.
5. Remaining portion of septum primum forms valve of foramen ovale.
6. (Not shown) Septum secundum and septum primum fuse to form the atrial
septum.
,7. (Not shown) Foramen ovale usually closes
soon after birth because of increased LA pressure.
Patent foramen ovale is caused by a failure of __________ and ___________ to
fuse after birth. What can this lead to? - ANSWERS--Caused by failure of
septum primum and septum secundum to fuse after birth; most are left
untreated.
-Can lead to paradoxical emboli (venous thromboemboli that enter systemic
arterial circulation), similar to those resulting from an ASD.
Septation of the ventricles (3 steps) - ANSWERS-1. Muscular ventricular
septum forms. Opening is called interventricular foramen.
2. Aorticopulmonary septum rotates and fuses with muscular ventricular
septum to form membranous interventricular septum, closing
interventricular foramen.
3. Growth of endocardial cushions separates atria from ventricles and
contributes to both atrial septation and membranous portion of the
interventricular septum.
What is the most common congenital cardinal anomaly? - ANSWERS-VSD
Most common location of VSD? - ANSWERS-The membranous septum
Bulbus cordis gives rise to __________. - ANSWERS-Smooth parts (outflow
tract) of left and right ventricles
Endocardial cushion gives rise to? - ANSWERS-Atrial septum ,membraneous
interventricular septum; AV & semilunar valves
,Primitive atrium gives rise to __________. - ANSWERS-Trabeculated
(muscular) portions of the left and right atria
Primitive ventricle gives rise to __________. - ANSWERS-Trabeculated
(muscular) portions of the left and right ventricles
Primitive pulmonary vein gives rise to __________. - ANSWERS-Smooth part
of the right atrium
Left horn of sinus venosus gives rise to __________. - ANSWERS-Coronary
sinus
Right horn of sinus venosus gives rise to __________. - ANSWERS-Smooth
part of the right atrium (sinus venarum)
Right common cardinal vein and right anterior cardinal vein gives rise to
__________. - ANSWERS-Superior vena cava (SVC)
When does the heart beat begin to beat spontaneously? - ANSWERS--4
weeks of development
-First functional organ in vertebrate embryos
Outflow tract formation - ANSWERS-Truncus arteriosus rotates; neural crest
and endocardial cell migrations cause truncal and bulbar ridges that spiral
and fuse to form aorticopulmonary septum to form ascending aorta and
pulmonary trunk.
What are the conotruncal abnormalities associated w/ failure of neural crest
cells to migrate? - ANSWERS-Transposition of the greta vessels
, Tetralogy of Fallot
Persistent truncus arteriosus
Aortic/pulmonary valves are derived from ____________. - ANSWERS-The
endocardial cushions of outflow tract.
Mitral/tricuspid valves are derived from __________. - ANSWERS-Fused
endocardial cushions of the AV canal.
Fetal erythropoiesis occurs in ___________? - ANSWERS--Yolk sac (3-8 weeks)
-Liver (6 weeks-birth)
-Spleen (10-28 weeks)
-Bone marrow (18 weeks to adult)
Hemoglobin development - ANSWERS--Embryonic globins: ζ and ε.
-Fetal hemoglobin (HbF) = α2γ2.
-Adult hemoglobin (HbA1) = α2β2.
-HbF has higher affinity for O2 due to less avid binding of 2,3-BPG, allowing
HbF to extract O2 from maternal hemoglobin (HbA1 and HbA2) across the
placenta.
Fetal circulation diagram - ANSWERS-
Blood in umbilical vein has a Po2 of _________ and is ________ saturated with
O2. - ANSWERS-≈ 30 mmHg, ≈ 80%
Umbilical arteries have _____ O2 saturation. - ANSWERS-Low
