The atria are the chambers that receive blood, and the ventricles are the chambers that pump blood.

There is one atrium and one ventricle on the right side and one atrium and one ventricle on the left side. In humans, the heart is about the size of a clenched fist it is divided into four chambers: two atria and two ventricles. Since the right side of the heart sends blood to the pulmonary circuit it is smaller than the left side which must send blood out to the whole body in the systemic circuit. The heart muscle is asymmetrical as a result of the distance blood must travel in the pulmonary and systemic circuits. The coronary circuit, which provides blood to the heart, is not shown. From the left ventricle, blood re-enters the systemic circuit through the aorta and is distributed to the rest of the body. From the pulmonary circuit, blood re-enters the heart through the left atrium. Blood then enters the pulmonary circuit, and is oxygenated by the lungs. Blood is pumped from veins of the systemic circuit into the right atrium of the heart, then into the right ventricle. The mammalian circulatory system is divided into three circuits: the systemic circuit, the pulmonary circuit, and the coronary circuit. The shorter distance to pump means that the muscle wall on the right side of the heart is not as thick as the left side which must have enough pressure to pump blood all the way to your big toe. For pulmonary and systemic circulation, the heart has to pump blood to the lungs or the rest of the body, respectively. Coronary circulation intrinsic to the heart takes blood directly from the main artery (aorta) coming from the heart.

The heart is a complex muscle that pumps blood through the three divisions of the circulatory system: the coronary (vessels that serve the heart), pulmonary (heart and lungs), and systemic (systems of the body). The information below was adapted from OpenStax Biology 40.3

Describe mechanisms for controlling heart rate and cardiac output.

Explain the process of electrical activation of the cardiac cycle.

Diagram and trace the structure and function of the mammalian heart, including all four chambers, valves, major blood vessels, and nodes essential for electrical conduction pathways.

Simple heart blood flow diagram