According to HowStuffWorks, blood flows into the right side of the heart and out to the body from the left side. During its passage, it passes through all four chambers of the heart. Between passing through the right and left sides of the heart, blood is pumped to the lungs for oxygenation.
Blood from the body is transported to the heart via the superior or inferior vena cava. These large veins drain the head and body, respectively, and empty into the heart through the right atrium. From the right atrium, blood drains through the tricuspid valve into the right ventricle. The right ventricle is more heavily muscled than the right atrium, according to HowStuffWorks, and has the power to push the blood out of the heart and into the lungs via the pulmonary arteries.
Blood returns from the lungs through the pulmonary veins and collects in the left atrium. From the left atrium, the oxygen-rich blood flows through the bicuspid valve into the left ventricle. The left ventricle is the thickest, strongest part of the heart. From this chamber, blood is pumped up through the aorta, which arcs over the heart. The aorta branches off into a network of smaller arteries that then carry the blood throughout the body.