Hemodynamics of VSDA VSD results in shunting of oxygenated blood from left to right because left ventricle has more pressure than right → Left to right shunt. Blood flow from left to right ventricle due to high pressure gradient → Pansystolic murmur and systolic thrill. Because left ventricle starts contracting before Right ventricle, pansystolic murmur starts early → Masking of Si. This pressure gradient is maintained throughout the systole pansystolic murmur lasts long → Masking of S2. Towards the end of systole, the declining left ventricular pressure becomes lower than aortic → Early closure of A2. Left to right shunt occurs during systole at a time when the right ventricle is also contracting, therefore left to right shunt streams to pulmonary artery more or less directly → No volume overload > Right ventricle size remains normal. Increased blood flow through pulmonary valve → Pulmonary ejection systolic murmur and delay & accentuated P2. Early closure of A2 and delayed closure of P2 cause → Widely split S2 (But this is usually masked by pansystolic murmur). Larger volume reaches the left atrium → Left atrial hypertrophy Increased blood flow through mitral valve → Accentuated S1 (But it is masked by pansystolic murmur) and delayed diastolic murmur.Note :Ejection systolic murmur of pulmonary valve can not be separated from pansystolic murmur. The effect of ejection systolic murmur is a selective transmission of pansystolic murmur to the upper left sternal border (pulmonary valve area) → In this area ejection characteristic of this murmur can be recognized since it does not mask the aortic component of S2. For the same reason second heart sound (S2) can be heard in the pulmonary area where it is not masked by pansystolic murmur.