Cardiac Cycle

1.       Heart contracts + relaxes in a rhythmic cycle.

2.     Cardiac cycle consists of alternating periods of :

·        Systole - contraction phase.

·        Diastole - relaxation phase.

3.     Cardiac cycle = one complete sequence of systole + diastole

4.     Resting adult - cardiac cycle repeated 72 times per minute = resting heart rate.

5.     Pulse = causes by elastic recoil of arteries.

6.     Ventricular pressure + aortic pressure + ventricular volume:

• changes (in response to the events that occur)
• at different phases of cardiac cycle.

7.     During diastole:

• pressure↓of heart chambers decreases
• volume↑ increases (as blood is pumped in).

8.     During systole:

• pressure↑of heart chambers increases
• volume↓ decreases (as blood is pumped out).

9.     When aortic pressure > ventricular pressure

à semilunar valves shut + vice versa.

10.  When ventricular pressure > atrial pressure

à AV valves shut + vice versa.

11.   Valves = ensure blood only flows in right direction.