With a vsd, why is the left heart overloaded?

VSD: With a VSD the blood shunts from the left ventricle back through the lungs to the left heart again. It forces the total volume pumped by the left ventricle to increase to maintain flow through the aorta. Pulmonary flow also increases and if pulmonary hypertension develops, biventricular failure can eventuate.

Vsd : Too much blood going from left to right and therefore tooucb blood to the lungs which return to left side of the heart and leads to left ventricular dilation ...