Patients with an uncomplicated ventricular septal defect remain asymptomatic. The diagnosis depends upon the characteristic murmur that is heard best at the lower left sternal edge. The murmur begins simultaneously with the first heart sound, indicating onset of flow out of the ventricles before opening of either the pulmonic or the aortic valve. Physical examination of a patient with an uncomplicated ventricular septal defect otherwise is entirely normal.
Differential diagnosis
The differential diagnosis of a systolic murmur beginning simultaneously with the first heart sound is either a ventricular septal defect, mitral regurgitation or tricuspid regurgitation.
The typical murmur of a ventricular septal defect is heard best between the lower left sternal edge and the mid precordium. It is caused by high velocity, turbulent flow across the defect from left ventricle to right ventricle. Flow occurs in this direction, because unless some other abnormality is present, left ventricular systolic pressure exceeds that of the right ventricle.
The murmur of mitral regurgitation is best heard at the apex. The murmur is usually higher in frequency and less noisy than that of a ventricular septal defect.
The murmur of tricuspid regurgitation is heard best at the lower left sternal edge. This murmur, like that of mitral regurgitation, also is higher in frequency and less noisy than that of a ventricular septal defect. Furthermore, the murmur of tricuspid regurgitation varies with respiration, being louder in inspiration. In addition, isolated tricuspid regurgitation is a rare abnormality in comparison with a ventricular septal defect.