Quantification of myocardial performance after regional ischemic injury is difficult because available performance indexes are markedly dependent on concurrent load changes. To develop a more load-insensitive index of myocardial function during ischemia, eight conscious dogs were instrumented to measure left ventricular pressure with micromanometers and myocardial segment length with ultrasonic dimension transducers. Preload was varied by transient vena caval occlusion during control conditions, after 15 min of coronary occlusion, and at intervals during 24 h of reperfusion. Acute ischemia shifted the linear relationship between segmental stroke work (SW) and end-diastolic segment length (EDL) rightward, diminishing the slope and increasing the chi-intercept. Preload recruitable work area (PRWA), defined as the area under the SW-EDL curve, reflected changes in both slope and intercept. During acute ischemia, conventional performance indexes and PRWA decreased significantly and required up to 24 h of reperfusion to return to control values. Of all parameters examined, PRWA was most responsive to prolonged ischemic dysfunction after reperfusion and was insensitive to concurrent load changes. Thus PRWA provides improved precision in quantifying of myocardial dysfunction after regional ischemic injury. This parameter should be especially useful in assessing the subtle effects of acute interventions designed to modify functional recovery.