Summarizes how a single drop of blood around the pulmonary and systemic circuits passes through the four chambers of the heart (the right atrium, the right ventricle, the left atrium, and the left ventricle) and is delivered throughout the body tissues. It is important to understand that both atria contract at the same time and both ventricles contract at the same time. Therefore, the heart works as two pumps, with the right and the left side working in a synchronized manner.