Semilunar valves The valves between the right and between the left ventricle ventricle and pulmonary arter and aorta consist of three cuplike ly cusps attached to the valve rings. PU At the end of the reduced ejection phase of ventricular systole, blood flow reverses briefly toward the ventricles. This flow reversal snaps the cusps together and prevents regurgitation of blood into the ventriclesThe valves between the right ventricle and pulmonary artery and between the left ventricle and aorta consist of three cuplike cusps attached to the valve rings. • Semilunar valves At the end of the reduced ejection phase of ventricular systole, blood flow reverses briefly toward the ventricles. This flow reversal snaps the cusps together and prevents regurgitation of blood into the ventricles