Five-Compartment Heart Model. Panel A shows the five-compartment heart model. An elastic pericardium encloses all four heart chambers. The dotted lines represent septal position when relaxed. Panel B is the equivalent hydraulic circuit model. Anatomical components of the equivalent circuit (LV = left ventricle, RV = right ventricle, LA = left atrium, RA = right atrium, SPT = interventricular septum, PERI = pericardium, TCV = tricuspid valve, MV = mitral valve, AOV = aortic valve, PAV = pulmonary valve). Specific pressures (PPL = pleural pressure, PPA = pulmonary arterial pressure, PAO = aortic pressure, PPERI = pericardial pressure, PRA = right atrial pressure, PLA = left atrial pressure, PRV = right ventricular pressure, PLV = left ventricular pressure).