First, unoxygenated blood enters the right atrium from the superior and inferior vanae cavae. Next the blood flows through the tricuspid valve into the right ventricle. From the right ventricle, the blood flows through the pulmonic valve into the pulmonary artery. The right and left pulmonary arteries then carry the unoxygenated blood to the right and left lungs for oxygen. The blood picks up a fresh supply of oxygen & releases carbon dioxide as waste. The now oxygenated blood flows through the pulmonary veins from the lungs into the left atrium. From the left atrium the blood flows through that bicuspid or mitral valve into the left ventricle. The left ventricle contracts, thus forcing blood through the aortic valve into the aorta for the distribution to the systemic circulation