Description
Each part of the cardiac cycle consists of several phases characterized by either a strong pressure change with constant volume or a volume change with a relatively small change in pressure.
Systole includes:
1.Isovolumic contraction.
2.Ejection.
Diastole includes:
3.Isovolumic relaxation.
4.Rapid ventricular filling.
5.Slow ventricular filling (diastasis).
6.Atrial contraction.
The duration of the cardiac cycle is inversely proportional to the heart rate. The cardiac cycle duration increases with a decrease in the heart rate and on the other hand it shortens with increasing heart rate. At a normal heart rate of 75 beats per minute, one cardiac cycle lasts 0.8 second. Under resting conditions, systole occupies ⅓ and diastole ⅔ of the cardiac cycle duration. At an increasing heart rate (e.g. during an intensive muscle work), the duration of diastole decreases much more then the duration of systole.