Assessment of right ventricular contractility by pressure-volume loop analysis. Presented are RV pressure-volume loops (dotted lines) in one representative animal at (a) baseline, in (b) pulmonary hypertension, and (c) 5 minutes after inhalation of iloprost. These were obtained during a controlled preload reduction by occlusion of the inferior caval vein. The end-systolic pressure-volume relationship is obtained by fitting a regression line (solid line) through the points of maximal (end-systolic) elastance, delineated for each cardiac cycle with grey circles. The induction of pulmonary hypertension elicits an immediate increase in RV contractility (as indicated by the increase in the slope of the end-systolic pressure-volume relationship), which serves the right ventricle to preserve pump performance without changing preload in the face of high afterload conditions (homeometric autoregulation). Conversely, treatment of pulmonary hypertension with inhaled iloprost obviates the need for homeometric autoregulation and allows the right ventricle to return to its baseline (lower) contractile state. RV, right ventricular.