Ans. is 'b' i.e., Ventricular ejection During ventricular ejection phase, when the steeply rising left ventricular pressure exceeds the aoic pressure (120 mm Hg), it is able to push open the aoic valve and eject the blad into the aoa, making the onset of ventricular ejection. PHASE OF CARDIAC CYCLE A cardiac cycle refers to the interval between onset of one heabeat to the onset of the next hea beat. It has two main phases : Ventricular systole and ventricular diastole. Ventricular systole (or simply systole) The systolic phase is divided into : - i) Isovolumetric contraction : As the ventricular contraction stas, the intraventricular pressure begins to rise, leading to an abrupt closure of AV valves (mitral and tricuspid valves). The closure of AV valves produces first hea sound (S1). the pressure is not enough to push open the semilunar valves (aoic and pulmonary) but causes the closed AV valve to bulge into the atrium, causing a small but sharp rise in atrial pressure called the 'C' wave on jugular venous pulse (JVP). Because both the valves (AV valves an semilunar valves) are closed, there is no change in volume, i.e., there is isovolumetric (isometric) contraction. Isovolumetric contraction ends with opening of semilunar (aoic and pulmonary) valves. ii) Ventricular ejection : When the steeply rising ventricular pressure exceeds the pressure in aoa and pulmonary aery, the semilunar valves open and ventricular ejection begins. The ejection of blood is rapid at first (rapid ejection phase), but slows down during later pa of systole (slow ejection phase). During rapid ejection phase, when the ventricles contract, the fibrous paition separating the ventricles from the atria (the AV ring) is pulled down. As a result, the atrial muscles get stretched and the atria dilate which causes a sharp fall in atrial pressure and the X-descent in JVP. iii) Protodiastole : In this very sho phase, ventricles sta relaxing and ventricular pressure begins to fall very sharply but the semilunar valves are still open. As a result, the column of blood in aoa (or pulmonary aery for right ventricle) tries to fall into the ventricle, hitting on its way the semilunar (aoic or pulmonary) valves. This causes closure of the aoic/pulmonary valves which produces 2" hea sound (S2). The venous blood flow continues to flow in the atria from great veins (SVC and ICC) and there is relaxation of fibrous AV ring due to ventricular relaxation; both of which cause a rise in atrial pressure and production of `V' wave in JVP. Ventricular diastole (or simply diastole) The diastole phase is divided into : - i) Isovolumetric relaxation : - This phase is the period between the closure of semilunar valve and opening of the AV valve. The ventricles continue relaxing and there pressure continues to fall. However, as both valves (AV valves and semilunar valves) are closed, there is no change in volume, i.e., isovolumetric relaxation. Relaxation phase ends with opening of AV valve. ii) Rapid ventricular filling : - When the ventricular pressure falls below atrial pressure, AV valves open and the accumulated blood in the atria rushes into the ventricle very rapidly. This passive filling contributes to 70% of ventricular filling, normally. This results in a sharp fall in atrial pressure which produces Y descent in JVP. iii) Diastasis : - After the initial rapid ventricular filling, blood flows slowly and smoothly from the SVC and IVC through the right atrium into the right ventricle without any turbulence anywhere along the path. Similarly, blood from the pulmonary veins flows into the left ventricle without any turbulence. This phase of nonturbulent ventricular filling is called diastasis. The atrial pressure remains slightly greater than the ventricular pressure because inflow to atrium exceeds the outflow the atrium. iv) Last rapid filling phase (atrial systole) : - The atria contract and pump blood rapidly into the ventricles.Atrial systole is associated with sharp rise in atrial pressure which produces a-wave in JVP.