The cardiac cycle begins with joint diastole. This means auricles and ventricles are in a relaxed position. This causes auriculoventricular valves (tricuspid and bicuspid valves) to open. Since ventricles are in relaxed position there is no pressure on semilunar valves and hence are closed. Thus blood from pulmonary veins and vena cava flows into left and right auricles and thus enters the ventricles. No blood flows out of the ventricles.