Although partial left ventriculectomy (PLV) was devised to reduce myocardial wall stress in patients with severe heart failure, whether the operation acutely improves cardiac pump function has not been determined either clinically or experimentally. Because precise control of preload, afterload, and heart rate is virtually impossible in animal experiments as well as clinically before and after surgery, we took advantage of the theoretical analysis to study quantitatively the changes in pump function by PLV. We reconstructed the endsystolic and end-diastolic pressure-volume relationships based on two different geometric conditions (i.e., before and after volume reduction) but from the same myocardial stress-strain relationship. The effect of volume reduction surgery on left ventricular pump function depended on preoperative conditions. We found that the improvement in pump function was achieved only if elastance (Ees) was low and if the end-systolic strain-axis scaling parameter (k) value was low. The presence of hypertrophy amplified the improved function, but again with low Ees and low end-systolic k. We conclude that the favorable hemodynamics are expected only in limited cases during the acute phase. Candidates for favorable preoperative factors include low end-systolic Ees, an end-systolic pressure-volume relationship being less convexed toward the volume axis (low k), and large left ventricular mass.