Cambridge (CIE) AS Biology Your notes
The Heart
Contents
Structure of the Heart
The Walls of the Heart
The Cardiac Cycle
Heart Action
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 1
, Structure of the Heart
Your notes
Mammalian Heart Structure
Heart structure
The human heart has a mass of around 300g and is roughly the size of a closed fist
The heart is a hollow, muscular organ located in the chest cavity
It is protected in the chest cavity by the pericardium, a tough and fibrous sac
The human heart diagram
The human heart has four chambers and is separated into two halves by the septum
The heart is divided into four chambers. The two top chambers are atria and the bottom
two chambers are ventricles
The left and right sides of the heart are separated by a wall of muscular tissue, called the
septum. The portion of the septum which separates the left and right atria is called the
interatrial septum, while the portion of the septum which separates the left and right
ventricles is called the interventricular septum
The septum is very important for ensuring blood doesn’t mix between the left and right
sides of the heart
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 2
, Valves in the heart
Valves in the heart: Your notes
Open when the pressure of blood behind them is greater than the pressure in front
of them
Close when the pressure of blood in front of them is greater than the pressure
behind them
Valves are important for keeping blood flowing forward in the right direction and
stopping it flowing backwards. They are also important for maintaining the correct
pressure in the chambers of the heart
The right atrium and right ventricle are separated by the atrioventricular valve, which is
otherwise known as the tricuspid valve
The right ventricle and the pulmonary artery are separated by the pulmonary valve
The left atrium and left ventricle are separated by the mitral valve, which is otherwise
known as the bicuspid valve
The left ventricle and aorta are separated by the aortic valve
There are two blood vessels bringing blood to the heart; the vena cava and pulmonary
vein
There are two blood vessels taking blood away from the heart; the pulmonary artery and
aorta
Coronary arteries
The heart is a muscle and so requires its own blood supply for aerobic respiration
The heart receives blood through arteries on its surface, called coronary arteries
It’s important that these arteries remain clear of plaques, as this could lead to angina or a
heart attack (myocardial infarction)
The outside of the human heart diagram
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 3
The Heart
Contents
Structure of the Heart
The Walls of the Heart
The Cardiac Cycle
Heart Action
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 1
, Structure of the Heart
Your notes
Mammalian Heart Structure
Heart structure
The human heart has a mass of around 300g and is roughly the size of a closed fist
The heart is a hollow, muscular organ located in the chest cavity
It is protected in the chest cavity by the pericardium, a tough and fibrous sac
The human heart diagram
The human heart has four chambers and is separated into two halves by the septum
The heart is divided into four chambers. The two top chambers are atria and the bottom
two chambers are ventricles
The left and right sides of the heart are separated by a wall of muscular tissue, called the
septum. The portion of the septum which separates the left and right atria is called the
interatrial septum, while the portion of the septum which separates the left and right
ventricles is called the interventricular septum
The septum is very important for ensuring blood doesn’t mix between the left and right
sides of the heart
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 2
, Valves in the heart
Valves in the heart: Your notes
Open when the pressure of blood behind them is greater than the pressure in front
of them
Close when the pressure of blood in front of them is greater than the pressure
behind them
Valves are important for keeping blood flowing forward in the right direction and
stopping it flowing backwards. They are also important for maintaining the correct
pressure in the chambers of the heart
The right atrium and right ventricle are separated by the atrioventricular valve, which is
otherwise known as the tricuspid valve
The right ventricle and the pulmonary artery are separated by the pulmonary valve
The left atrium and left ventricle are separated by the mitral valve, which is otherwise
known as the bicuspid valve
The left ventricle and aorta are separated by the aortic valve
There are two blood vessels bringing blood to the heart; the vena cava and pulmonary
vein
There are two blood vessels taking blood away from the heart; the pulmonary artery and
aorta
Coronary arteries
The heart is a muscle and so requires its own blood supply for aerobic respiration
The heart receives blood through arteries on its surface, called coronary arteries
It’s important that these arteries remain clear of plaques, as this could lead to angina or a
heart attack (myocardial infarction)
The outside of the human heart diagram
© 2025 Save My Exams, Ltd. Get more and ace your exams at savemyexams.com 3
