What happens during cardiac tamponade?

• A. Dilates the ventricles
• B. Compression of the heart by fluid
• C. Increases heart rate only
• D. Reduces blood viscosity

Answer: (B)

The key idea is that excess fluid in the pericardial sac presses on the heart and prevents it from filling properly. In cardiac tamponade, the accumulating fluid creates external pressure that limits diastolic expansion of all chambers, so about one heartbeat after another the ventricles can’t fill adequately. That reduced filling lowers stroke volume and cardiac output, leading to low blood pressure. Because the heart’s filling is compromised, venous return backs up, often causing elevated jugular venous pressure, and you may hear muffled heart sounds with possible pulsus paradoxus in some cases. Tachycardia can occur as the body tries to maintain perfusion, but the defining issue is the external compression of the heart by fluid, not a primary dilation, a constant and sole increase in heart rate, or a change in blood viscosity.