Which statement about pericardial effusion is true?

• A. It is a blood clot in the pericardial space
• B. It is air in the pericardial space
• C. It is inflammation only with no fluid
• D. It is a collection of fluid in the pericardial space

Answer: (D)

Pericardial effusion is a collection of fluid in the pericardial space between the layers of the pericardium. This distinguishes it from a blood clot in that space (hematopericardium) or air in the space (pneumopericardium). It also differs from pericarditis without fluid, where inflammation occurs but no fluid accumulates. When fluid builds up, it can impede the heart’s ability to fill properly, potentially leading to reduced cardiac output and, if rapid or large, cardiac tamponade. Clinically, this is assessed with imaging like echocardiography, and treatment focuses on removing the fluid if the patient is symptomatic or unstable, while addressing the underlying cause.