During complete cardiopulmonary bypass, intercardiac return primarily comes from which venous source?

• A. Bronchial veins
• B. Pulmonary veins
• C. Coronary sinus
• D. Superior vena cava

Answer: (A)

The key idea is that the blood returning to the bypass circuit from within the heart comes mainly from the myocardium’s own venous drainage. The coronary veins collect venous blood from the heart muscle and funnel it through the coronary sinus, which empties into the right atrium. Even when the heart is arrested and the pulmonary circulation is bypassed, this coronary venous blood continues to drain into the right atrium and becomes part of the venous return feeding the CPB circuit. That makes the coronary sinus the primary source of intercardiac return.

Bronchial veins do drain part of the systemic circulation via the azygos system, but they are not the main intracardiac source of venous return. Pulmonary veins carry oxygenated blood from the lungs to the left atrium, not into the CPB venous circuit. The superior vena cava is a major conduit for systemic venous return, but the question specifically concerns intracardiac (within the heart) return, which is driven by the coronary sinus.