Background.In heart transplants, left ventricular function may be impaired in the absence of rejection or graft atherosclerosis. Matching between left ventricle and arterial receptor, i.e., ventriculoarterial coupling, and left ventricular efficiency have never been studied.Methods.Left ventricular pressure-volume loops and single beat analysis were used to determine effective arterial elastance (Ea) and the slope of the end-systolic pressure-volume relation (end-systolic elastance; Ees). Left ventricular efficiency was evaluated by determination of external work (EW), pressure-volume area (PVA), coronary blood flow (continuous thermodilution), and myocardial oxygen consumption (MVO2). Measurements were made at baseline in 11 control subjects and 9 heart transplant recipients (HTX) without rejection and were repeated after phenylephrine in the latter group.Results.At baseline, Ees, Ees/Ea, and work efficiency (EW/PVA) were lower in HTX than in control subjects (2.51±0.87 vs. 3.70±1.15 mmHg/ml/m2,P<0.01; 0.96±0.21 vs. 1.47±0.31,P<0.001; and 0.53±0.08 vs. 0.59±0.09,P<0.01, respectively). Energy conversion efficiency (PVA/MVO2) and mechanical efficiency (EW/MVO2) were higher in HTX (0.58±0.08 vs. 0.45±0.14,P<0.001; and 0.31±0.05 vs. 0.26±0.06,P<0.001, respectively). In HTX, phenylephrine infusion increased Ees, Ea, EW, PVA, and MVO2without modifying Ees/Ea, EW/PVA, PVA/MVO2, and EW/MVO2.Conclusions.In heart transplants, (1) left ventricular contractility is moderately depressed; (2) elevation of energy conversion efficiency compensates for the decrease in work efficiency, allowing normal mechanical efficiency; and (3) alpha 1 adrenergic stimulation does not impair ventriculoarterial coupling and mechanical efficiency.