Question

why two of the valves in heart are close​

Answer 1

They close to keep blood from flowing backward during the other half of the heartbeat. The mitral valve has only two leaflets; the aortic, pulmonic and tricuspid valves have three. The leaflets are attached to and supported by a ring of tough, fibrous tissue called the annulus.

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Answer 2

the valves prevent the backward flow of blood. These valves are actual flaps that location on each of the two ventricles.