The normal number of chambers in a healthy human heart is four: two atria and two ventricles. The right atrium and right ventricle handle oxygen-poor blood, while the left atrium and left ventricle handle oxygen-rich blood.
Blood returning from the body enters the right atrium through the superior and inferior venae cavae. It moves into the right ventricle and is pumped through the pulmonary artery to the lungs. Oxygenated blood then returns to the left atrium through the pulmonary veins, passes into the left ventricle, and leaves through the aorta to supply the body.
The atria are the upper receiving chambers; the ventricles are the lower pumping chambers. Septa separate the right and left sides, helping prevent oxygen-rich and oxygen-poor blood from mixing. Four valves keep blood moving in one direction.
A common mix-up is confusing chambers with valves: the heart has four chambers and also four main valves. Some congenital heart defects can alter the structure, but four chambers is the normal human arrangement.