Is the dub sound heard during atrial or ventricular diastole?

The "dub" sound, or the second heart sound (S2), is primarily associated with ventricular diastole. It occurs when the aortic and pulmonary valves close at the end of ventricular contraction, marking the transition to diastole when the ventricles relax and fill with blood. In contrast, the "lub" sound (S1) occurs during atrial diastole, when the atrioventricular valves close as the ventricles begin to contract.