ventricular septal defect
A ventricular septal defect is a hole in the muscular wall between the two pumping chambers, the ventricles. If the atrial defect is a gap between two upstairs rooms, this is a gap between the two powerful engine rooms below, where pressures are far higher. Because the left ventricle squeezes much harder than the right, blood is driven forcefully through the hole from left to right.
This left-to-right shunt sends extra blood into the lungs with each beat. A small defect produces a loud murmur but little harm and often closes by itself in early childhood. A large defect floods the lungs, causes fast breathing and poor weight gain in infancy, and, if left untreated for years, can raise lung blood pressure until the shunt eventually reverses.
Ventricular septal defects are among the most common congenital heart defects. Small ones are simply watched; large or symptomatic ones are repaired surgically or, in selected cases, with a catheter device, ideally before irreversible lung changes develop.
An infant with a harsh holosystolic murmur at the left lower sternal border and failure to thrive is diagnosed with a large ventricular septal defect and scheduled for surgical closure.
A harsh holosystolic murmur at the left sternal border is typical of a ventricular septal defect.
Counterintuitively, a small ventricular septal defect often makes a louder murmur than a large one, because the narrow opening forces a faster, more turbulent jet of blood across it.