diastol

Diastol, also known as diastole, is the relaxation phase of the cardiac cycle during which the ventricles repolarize and fill with blood after systole. It begins after the closure of the aortic and pulmonary valves and ends with the onset of the next ventricular contraction. The diastolic interval comprises several subphases: isovolumetric relaxation, rapid ventricular filling, diastasis, and atrial systole, when the atria contract to augment ventricular filling. During most of diastole the mitral and tricuspid valves are open, allowing blood to flow from the atria into the ventricles.

During diastole the ventricular pressure falls below atrial pressure, enabling filling, and the aortic and pulmonary valves remain closed. The heart’s coronary arteries receive most of their blood flow during diastole, when the myocardium is relaxed and not compressed by ventricular contraction. The dicrotic notch on arterial pressure tracings marks the moment of aortic valve closure at the start of diastole. The duration of diastole varies with heart rate; at higher heart rates, diastole shortens more than systole, which can reduce ventricular filling time and coronary perfusion.

Clinical relevance includes diastolic dysfunction, where impaired relaxation or increased stiffness of the ventricles leads to elevated filling pressures and symptoms of heart failure with preserved ejection fraction (HFpEF). Diastolic function is commonly assessed with echocardiography, using measures such as the E/A ratio, tissue Doppler E' velocity, and the E/e' ratio to estimate filling pressures and assess relaxation.

Diastol is the counterpart to systol, the contraction phase in which the ventricles eject blood into the aorta and pulmonary artery.