The heart consists of four chambers in which blood flows. Blood enters the right atrium and passes through the right ventricle. The right ventricle pumps the blood to the lungs where it becomes oxygenated. The oxygenated blood is brought back to the heart by the pulmonary veins which enter the left atrium.
D. Right ventricle A muscle contraction forces the blood through the tricuspid valve in the right ventricle. When the right ventricle contracts, blood is forced through the pulmonary semilunar into the pulmonary artery.
