Explain the Cardiac Cycle

Deoxygenate blood from the body drains into the right atrium of the heart through the superior and inferior vena cave vessels. When the atria contract, blood is squeezed through the tricuspid valve into the right atrium. When the ventricles contract, the blood travels from the right ventricle, through the pulmonary arteries and into the lungs, where it gets oxygenated.
Once the blood is oxygenated, it returns to the heart through the pulmonary veins, and into the left atrium. When the atria contract, the blood is squeezed through the bicuspid valve into the left ventricle. When the ventricles contract, the blood travels from the left ventricle, through the aorta and to the rest of the body. The oxygenated blood is then able to supply the organs, muscles and tissues of the body with oxygen.