= Pulmonary valve
The \b[pulmonary valve] is the <heart valve> between the <right ventricle> and <pulmonary trunk>. During forward ventricular ejection it allows <blood> to enter the <pulmonary circulation>; closure limits return from the <pulmonary trunk> into the relaxing <right ventricle>.<How Blood Flows through the Heart by NHLBI>[Heart valves]{ref}
Its pocket-like cusps respond to the changing <pressure> difference. Unlike the <tricuspid valve>, the <pulmonary valve> has no attached <chordae tendineae> or <papillary muscles>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§19.1, Heart Valve Structure and Function, pulmonary semilunar valve]{ref} Thus the same direction-control task is achieved by different supporting structures at the chamber inlet and outlet.
A deliberately idealized valve model sets forward <blood flow> to zero when the downstream <pressure> exceeds the upstream <pressure>, and permits positive flow when ventricular <pressure> exceeds trunk <pressure>. This model captures direction but omits the inertia and deformation of real cusps. It is useful for checking the sign of a flow term, not for predicting an exact opening time.
For example, if a constructed cycle sends 80 mL forward and 10 mL backward across the <pulmonary valve>, net transport is 70 mL. Counting only the positive part of <blood flow> overestimates net delivery. This is why <stroke volume> inferred from changing chamber volume and net forward flow in the <pulmonary trunk> require compatible assumptions about valve function.
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