Blood enters the heart through 2 big veins called the Inferior and Superior Vena Cava. They empty deoxygenated blood from the body into the right atrium. It, then, flows from your right atrium into your right ventricle through the tricuspid valve. When the ventricle is full, the valve shuts, preventing blood from flowing back. As the ventricle contacts, the blood leaves the heart through the pulmonary valve, into the pulmonary artery and to the lungs where it gets oxygenated.