Left-to-right shunt in VSD

Steps:

• Left ventricle contains oxygenated blood under higher pressure than right ventricle with deoxygenated blood.
• VSD allows blood to flow from higher-pressure left ventricle to lower-pressure right ventricle.
• This shunts oxygenated blood into the right ventricle.
• Oxygenated blood then exits right ventricle via pulmonary artery to lungs.

Why C is correct:

• Higher left ventricular pressure drives oxygenated blood through VSD into right ventricle and pulmonary artery, per pressure gradient principle in congenital heart defects.

Why the others are wrong:

• A: Pulmonary vein carries oxygenated blood from lungs to left atrium; VSD affects ventricles, not veins.
• B: Shunt occurs between ventricles, not into right atrium upstream.
• D: Left-to-right shunt predominates, preventing deoxygenated blood from entering left atrium.

Final answer: C