Coupled Pump Model of Heart. Panels 1A,C-D show coupled "pump model" of the human heart, with its chamber volumes and pressures. Panel 1B shows hydraulic equivalent circuit model, with diode-resistance pairs representing the pressure-dependent behavior of the tricuspid and mitral (inlet) valves RTC and RM; and the pulmonic and aortic (outlet) valves RPAp and RAOp. Time-varying compliances of the right atrium (RA), right ventricle (RV), left atrium (LA), left ventricle (LV), and septum (SPT) are included. The compliance of the pericardium (CPERI) is time-invariant.