The heart’s four chambers function as a double-sided pump. The heart needs to work at just the right rhythm. It is divided into right and left halves. These halves are further divided into atria and ventricles. The right ventricle pumps blood to the lungs whereas the left ventricle pumps blood to everywhere else in the body. For this reason, the left ventricle has the thickest muscle mass of all the chambers.

Veins carry blood both to the right and left atria at the same time. The cycle begins when the two atria contract, which pushes blood into the ventricles. After this, the ventricles contract, which forces the blood out of the heart.

The valves between the atria and the ventricles prevent blood from returning to the ventricles. When the heart is resting between its beats, the valves between the ventricles and arteries prevent the blood from flowing back into the heart. However, there are no valves between the atria and the veins.

The structure of the heart.