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How do the mitral and tricuspid valves prevent blood from flowing backward?

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Illustration of a human heart cross-section showing four chambers-left and right atria and ventricles-with labeled major blood vessels. An inset highlights cardiac muscle tissue, showing myocytes and intercalated disks. — human cardiovascular system The human heart is both a pump and a muscle. Its four chambers move blood efficiently, while cardiac muscle cells joined by intercalated disks synchronize each contraction.

The mitral and tricuspid valves prevent the backflow of blood from the ventricles into the atria through a coordinated mechanical process. When the ventricles contract, blood is forced backward against the valve leaflets, pushing them upward until they meet and unite to form a complete partition.1

To ensure these flaps do not open into the atria, they are restrained by chordae tendineae—tendinous cords of dense tissue—that connect the leaflets to papillary muscles within the ventricular walls. These structures limit the extent to which the valve margins can billow toward the atria, effectively securing the seal during ventricular contraction. While the tricuspid valve consists of three flaps and the mitral valve consists of two, both function as essential one-way gates that maintain the unidirectional flow of blood through the human cardiovascular system.12