The four valves of the heart include the tricuspid valve, the mitral vale, the pulmonary valve and the aortic valve. The tricuspid valve lies between the right atrium and the right ventricle and opens to allow blood to flow into the right ventricle from the right atrium. The mitral valve lies between the left atrium and the left ventricle. This valve allows blood to flow into the left ventricle from the left atrium. The pulmonary valve connects the heart to the lungs and allows blood to flow out of the right ventricle into the lungs.
The aortic valve connects the heart to the systemic circulation and allows blood to flow from the left ventricle to the rest of the body. The four chambers of the heart do not contract at the same time. They contract separately to push blood through the heart, lungs and throughout the entire body. As the heart chambers relax, they are in diastole. As they contract, they are in systole.