This study was performed to determine whether preload-adjusted peak power can act as a surrogate for preload-adjusted maximal power in the assessment of left ventricular performance in the clinical setting. Ninety-nine consecutive patients who had undergone elective coronary artery bypass grafting were studied. Fifty-five of these patients were divided into four study groups. Afterload was changed with phenylephrine (n = 12) or glyceryl trinitrate (n = 13), preload was increased with intravenous colloid (n = 18), and contractility was increased with dobutamine (n = 12). There was excellent correlation between the two indices (r = 0.99, y = 1.0168x + 0.0769; p < 0.0001). Manipulation of neither preload nor afterload affected the indices. Both indices increased significantly during dobutamine infusion (p = 0.002). In conclusion, preload-adjusted peak power can be used as a substitute for preload-adjusted maximal power in the determination of ventricular performance in clinical practice.