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  • tissue
  • These valves have tissue flaps that open and close with each heartbeat. (nih.gov)
  • These valves may not have enough tissue flaps, they may be the wrong size or shape, or they may lack an opening through which blood can flow properly. (nih.gov)
  • heart's
  • As the blood builds up in the atria, these valves open to allow blood to flow into the ventricles (the heart's two lower chambers). (nih.gov)
  • blood flows
  • The blue arrow shows the direction in which oxygen-poor blood flows through the heart to the lungs. (nih.gov)
  • The red arrow shows the direction in which oxygen-rich blood flows from the lungs into the heart and then out to the body. (nih.gov)
  • As a result, not enough blood flows through the valve. (nih.gov)