Diastole

Diastole is the portion of the cardiac cycle during which the heart muscle relaxes and the chambers fill with blood. In the ventricles, diastole begins after the heart valves that open during systole close (the second heart sound) and ends with the onset of the next ventricular contraction. The diastolic phase includes isovolumetric relaxation, rapid ventricular filling, diastasis, and atrial systole. During isovolumetric relaxation the ventricles relax with all valves closed; when the mitral and tricuspid valves open, blood flows rapidly from the atria into the ventricles, producing the early diastolic filling phase. Diastasis follows, during which filling slows, and in late diastole the atria contract (atrial systole) to deliver a final boost of blood into the ventricles.

Ventricular filling is governed by ventricular compliance and relaxation. A healthy heart efficiently lowers ventricular pressure during early diastole; as a result the filling is rapid and the left atrial pressure remains low. Factors that increase stiffness or impair relaxation—such as aging, hypertension, myocardial disease—can reduce diastolic filling and raise filling pressures.

Clinically, diastolic function is assessed by echocardiography and other imaging methods. Diastolic dysfunction can occur with preserved ejection fraction (HFpEF) or reduced EF, and is influenced by heart rate, loading conditions, and atrial contractility. Doppler measurements of E and A waves, and tissue Doppler e' velocities, help estimate filling pressures. Management focuses on addressing underlying conditions and maintaining normal heart rate and blood pressure to optimize diastolic filling.