The fluid-filled space that helps reduce the friction of a beating heart is called the:

A) endocardium.
B) pericardial cavity.
C) interventricular septum.
D) fossa ovalis.
E) auricle.

Pericardial Cavity

A fluid-filled space between the pericardium (the membrane that surrounds the heart) and the heart itself.

Beating Heart

A term describing the continuous rhythmic contraction and relaxation of the heart muscle, which pumps blood through the circulatory system.

Friction

The resistance that one surface or object encounters when moving over another, a fundamental force that opposes the relative motion or tendency of such motion of two surfaces.