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Figure 1 Changes in left ventricular (LV) pressure-segment length loops during ischemia and increase in afterload from a representative experiment. The isovolumic contraction (IVC) and isovolumic relaxation (IVR) phases are indicated. The loops during baseline and left anterior descending coronary artery (LAD) stenosis rotate counterclockwise, indicating net actively contracting segments. During LAD occlusion the loops rotate clockwise, indicating that the segment behaves passively during systole. Aortic constriction superimposed on LAD stenosis changed segment behavior from active to passive.