= Valve leaflet
A \b[valve leaflet] is a mobile tissue flap forming part of a <heart valve>. Its movement and contact with neighboring leaflets help permit forward <blood flow> while limiting backward flow. The supporting <cardiac valve annulus>, the <pressure> difference and the leaflet's geometry all contribute to its behavior. The meeting of leaflet surfaces that closes a valve is called <coaptation>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§19.1, Heart Valve Structure and Function]{ref}
The <mitral valve> and <tricuspid valve> have leaflets supported by <chordae tendineae> and <papillary muscles>. The <aortic valve> and <pulmonary valve> instead have pocket-like cusps without that chordal apparatus. A leaflet is therefore a functional part of a particular valve structure, not an isolated rigid door.
An original force estimate illustrates the loading scale. A uniform <pressure> difference $\Delta p$ over an effective area $A$ gives a resultant $F=\Delta pA$. For stipulated $\Delta p=12$ kPa and $A=2$ cm$^2$, $F=2.4$ N. Doubling the area at the same <pressure> doubles this resultant, but it does not specify how the load is divided among attachments or distributed as tissue <stress>.
A primary left-heart simulator experiment measured <chordae tendineae> forces while moving <papillary muscles> and found responses that depended on the chordal type.<Effects of papillary muscle position on chordal force distribution: an in-vitro study by Jorge Hernan Jimenez and others>[Abstract, Methods and Results]{ref} This gives a concrete reason to examine leaflet geometry and supporting connections together. Complete <coaptation> is a contact-and-motion condition; an accurate measurement of one chordal force does not by itself show that the entire valve seals.
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