Schematic diagram of the heart.
Oxygenated blood is red, deoxygenated blood is blue.
Figure 2 shows a schematic representation of fluid flow through the heart, Figure 3 shows the heart's pumping cycle. Deoxygenated blood flows from the body into the right atrium. The right atrium then contracts, forcing blood into the expanding right ventricle. Next, the ventricle contracts, pushing blood toward the lungs. Oxygen-rich blood leaves the lungs and returns to the heart through the left atrium.