What is a flap of tissue in the heart that acts like a one way door?

Valves are the thin flat tissues in the heart that acts like a one way door. The valves serve the role of preventing the back flow of blood. The heart has four major valves; that is the tricuspid valve located between the right atrium and the right ventricle, Pulmonary valve at the right ventricle and the pulmonary artery, bicuspid valve located between the left atrium and the left ventricle, and the aortic valve at the base of the aorta.