The document describes the structure and function of the mammalian heart. It has an external muscular structure made of cardiac muscle that weighs around 300g. Internally, it has four chambers separated by valves that control blood flow. The heart has a double circulatory system where blood is pumped from the heart to the lungs and throughout the body in separate loops. Each heartbeat, known as the cardiac cycle, involves a precise sequence of electrical signals and contractions that pump blood efficiently.

1. The Mammalian Heart
External and Internal Structure
Mass = 300 g
Muscle = Cardiac muscle
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2. Cardiac muscle
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3. A mammalian heart seen from the
front (External)
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4. Coronary arteries
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5. Vertical section through a
mammalian heart (Internal)
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6. Vertical section through a
mammalian heart (Internal)
(mitral)
• septum
• papillary
muscle
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7. Atrio-ventricular valves
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8. Difference in thickness of the
walls of different chambers and
their functions?
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9. Mammalian circulatory system
Closed double
circulation
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10. Cardiac cycle
* Sequence of events which makes up one heart beat
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11. Heart action control
 Myogenic – naturally contracts and relaxes, not
needing to receive impulses from a nerve to make it
contract
 Important components:
i) sinoatrial node (SAN/pacemaker) – sets the rhythm of
contraction for all other cardiac muscle cells
ii) atrio-ventricular node (AVN) – picks up the excitation
wave as it spreads across the atria and passes it on to
Purkyne tissue
iii) Purkyne tissue – conducting fibres that transmits
excitation wave through ventrical walls
 Fibrillation – heart wall flutters rather than contracting
as a whole and then relaxing as a whole (started by
electric shock or by damage to large areas of muscle in
the walls of the heart)
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12. Fibrillation
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13. Heart action control
Purkyne tissue
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14. Electrocardiogram (ECG)
 Electrodes placed over opposite sides of
the heart and the electrical potentials
generated recorded with time
 ECG – graph of voltage against time
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