The cycle of the heart in its diastole (relaxation) state and its systole (contraction) state. The ventricles can be in a diastolic state, while the atria can be in a systolic state. An auricle is a small conical projection coming out of the atrium, but in some texts it represents the actual atrium. As the heart relaxes, blood enters from the other side and into the atria, then leaves and enters the ventricles. When the heart contracts, blood leaves the ventricles and goes back into the body.
Thomson, J. Arthur The Outline of Science volume II (New York, NY: G.P. Putnam's Sons, 1922)
Courtesy the private collection of Roy Winkelman