Heart, Front View

The external structures of the heart include the ventricles, atria, arteries and veins. Arteries carry blood away from the heart while veins carry blood into the heart. The vessels colored blue indicate the transport of blood with relatively low content of oxygen and high content of carbon dioxide. The vessels colored red indicate the transport of blood with relatively high content of oxygen and low content of carbon dioxide.

Pericardium

The pericardium is a thin double-layered sac which encloses the heart. Fluid is contained within the layers and lubricates the constantly rubbing surfaces.

Cardiac Tamponade

Cardiac tamponade is a condition involving compression of the heart caused by blood or fluid accumulation in the space between the myocardium (the muscle of the heart) and the pericardium (the outer covering sac of the heart). Blood or fluid collects within the pericardium. This prevents the ventricles from expanding fully, so they cannot adequately fill or pump blood. Cardiac tamponade is an emergency condition that requires hospitalization.