Chamber Pressure-Volume Relationships using Different Septal Models. P-V relationships for the four cardiac chambers shown for three septal model cases – case a: passive septum with ESPVR only (red); case b: passive septum with EDPVR only (blue); case c: active septum with ESPVR and EDPVR modulated by an activation function (see text for details). For case a, the stiff, unstressed septum reduces VLV, increasing end-diastolic PLV and restricting LV filling, while increasing systolic PRV due to no leftward movement, and not contributing to RV ejection. In case b, the less-compliant, rightward-shifted septum expands VLV and reduces VRV overall, increasing systolic PRV and contributing little to ventricular ejection (Panels C-D). In both cases, the reduced cardiac output decreases PRA (Panel A) and end-diastolic PRV (Panel C). Reduced stroke volume causes blood to accumulate in the pulmonary bed, increasing PLA (Panel B).