What best describes pericardial effusion?

Pericardial effusion is best described as the build-up of fluid between the pericardium and the heart. The pericardium is a double-walled sac that surrounds and protects the heart, and when excess fluid accumulates in the space between the heart and this outer layer, it can lead to a number of important cardiovascular issues.

This condition can result from various causes, including infections, inflammatory diseases, trauma, or malignancies. The presence of excess fluid can increase pressure in the pericardial space, potentially leading to complications such as cardiac tamponade, where the heart's ability to fill with blood is impaired because of the pressure from the fluid.

Other options provided align with different processes: fluid build-up between the heart and lungs pertains to pleural effusion, accumulation of blood within the heart muscle refers to myocardial hemorrhage or other cardiac conditions, and fluid build-up in the coronary arteries is not a recognized medical condition. Understanding the mechanisms and locations of effusions is crucial for diagnosis and treatment in cardiovascular medicine.