What is the effect of a patent ductus arteriosus (PDA) on left ventricular preload?

A patent ductus arteriosus (PDA) allows blood to flow between the aorta and the pulmonary artery, resulting in a left-to-right shunt. This creates a situation where some of the oxygenated blood from the aorta bypasses the systemic circulation and returns to the lungs instead.

As a result of this shunting, there is an increase in blood volume returning to the left atrium since more blood is effectively coming back from the lungs due to the PDA shunt. The left ventricle, therefore, experiences an increase in preload, which is the volume of blood in the ventricles at the end of diastole. This increased return of blood can lead to dilatation and eventual hypertrophy of the left ventricle if the PDA remains patent and not addressed. Hence, the correct answer is that the presence of a patent ductus arteriosus increases left ventricular preload significantly.