= Tricuspid valve
The \b[tricuspid valve] is the right atrioventricular <heart valve>, between the <right atrium> and <right ventricle>. It permits filling from the <right atrium> and limits backward <blood flow> during ventricular contraction.<How Blood Flows through the Heart by NHLBI>[Heart valves]{ref}
The leaflets are supported by <chordae tendineae> attached to <papillary muscles>. Rising ventricular <pressure> brings the leaflets together; tension in the supporting apparatus helps prevent their displacement into the <right atrium>. The <papillary muscles> do not need to pull the leaflets open to initiate filling.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§19.1, Right Ventricle and Heart Valve Structure and Function]{ref}
A useful mechanical analogy is a pressure-loaded flap restrained by tethers. The <pressure> difference supplies a load, while the tethers limit how far the flap can move. The analogy distinguishes the role of the <chordae tendineae> from the action of a motorized door.
The valve also determines how to interpret <right ventricular ejection fraction>. Suppose a constructed ventricular contraction reduces cavity volume by 80 mL, but 20 mL of that loss returns through the <tricuspid valve> into the <right atrium>. Only 60 mL remains for forward transport through the <pulmonary valve>, if other transfers are negligible. The measured cavity-volume change is still 80 mL. An ejection fraction calculated from chamber volumes therefore does not by itself measure the useful forward <stroke volume> of the <pulmonary circulation>.
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