Blood enters the heart through the superior vena cava and the inferior vena cava into the right atrium. When the right atrium contracts, this poor oxygen blood flows to the right ventricle through the tricuspid valve. The valve then closes and the right ventricle contracts ejecting blood through the pulmonary trunk and pulmonary arteries to the lungs to be oxygenated.
Pulmonary veins carry oxygen-rich blood from the lungs into the left atrium. Then the atrium contracts and blood flows from your left atrium into your left ventricle through the mitral valve. The valve then closes, the left ventricle contracts and blood leaves the heart through the aortic valve, into the aorta and to the body.
