We studied three isovolumic indexes of contractility, i.e., dP/dtmax, dP/dtDP40, and (dP/dt)/TPmax, in normal dogs and in a matched group of chronically hypertensive dogs with left ventricular hypertrophy (LVH) [DP40, developed LV pressure of 40 mmHg; TP, total LV pressure above atmospheric]. The LVH was moderate in degree with the LV-to-body weight ratio 50% greater than in normal dogs. The experiments were performed under pentobarbital with open chest, autonomic blockade, and independent control of mean left atrial pressure (LAP) and mean aortic pressure (MAP). We found that dP/dtmax provided the most consistent comparison of inotropic state in the two groups under both basal conditions and with norepinephrine (NE). The other indexes occurred too early in systole to reflect complete LV activation, particularly during the infusion with NE. Under controlled conditions basal dP/dtmax of LVH dogs was 1.28 times the value of normal dogs, with the increase accounted for by the amplifier effect of the increase in LV mass. But with moderate lowering of aortic pressure, inotropic state was more easily compromised in LVH than in normal dogs. With steady-state stimulation by infusing increasing amounts of NE, dP/dtmax rose by 10 times basal in both LVH and normal dogs at maximum stimulation. The absolute value of the index was 1.31 times higher in the LVH group, with the amplifier effect thus the same as under basal conditions. The results suggest that basal and maximal inotropic states are normal in LVH under optimum loading conditions.