Blood flow enters the heart from the venous circulation through the vena cava, which empties into the right atrium. Flow then proceeds from the right atrium, through the tricuspid valve to the right ventricle during diastole. Systolic flow occurs with blood ejection from the right ventricle through the pulmonic valve to the main pulmonary artery. The right and left pulmonary arteries then carry the blood to the lungs.