The venous return to the right ventricle (RV) increases during inspiration due to negative intrathoracic pressure and P2 is even more delayed, so it is normal for the split of the second heart sound to widen during inspiration and to narrow during expiration. In addition, the more muscular and stiff "less compliant" left ventricle (LV) empties earlier than the right ventricle. This higher closing pressure leads to earlier closure of the aortic valve. The closing pressure (the diastolic arterial pressure) on the left is 80 mmHg as compared to only 10 mmHg on the right. S2 is normally split because the aortic valve (A2) closes before the pulmonary valve (P2). The second heart sound (S2) represents closure of the semilunar (aortic and pulmonary) valves (point d). S1 is normally a single sound because mitral and tricuspid valve closure occurs almost simultaneously. The first heart sound (S1) represents closure of the atrioventricular (mitral and tricuspid) valves as the ventricular pressures exceed atrial pressures at the beginning of systole (point a).
Corrected Transposition of the Great Arteries (L-TGA).Complete Transposition of the Great Arteries (D-TGA).Systolic Murmur Grades based on the intensity of the murmur.