diastolé

Diastole is a fundamental phase of the cardiac cycle, representing the period when the heart muscle relaxes and the heart chambers fill with blood. It is one of the two main stages of the heartbeat, the other being systole, which is the contraction phase. During diastole, the atria and ventricles are at rest.

The cardiac cycle begins with diastole, specifically atrial diastole, where the atria relax. Following this, ventricular diastole occurs. This involves the relaxation of the ventricles, which leads to a decrease in pressure within these chambers. As ventricular pressure drops below atrial pressure, the atrioventricular valves, namely the mitral and tricuspid valves, open. This allows blood to flow passively from the atria into the ventricles. This phase of passive filling accounts for a significant portion of the ventricular volume.

As diastole progresses, the ventricles continue to fill. Towards the end of diastole, atrial contraction, known as atrial systole, occurs. This active atrial contraction pushes any remaining blood from the atria into the ventricles, ensuring they are maximally filled before the next contraction. However, even without atrial contraction, the ventricles would still fill to about 70-80% of their capacity passively. The duration of diastole is influenced by heart rate; at slower heart rates, diastole is longer, allowing for more complete ventricular filling, which can increase stroke volume and cardiac output.