The remodeling of the spared non-ischemic left ventricular myocardium after different time intervals from the occlusion of the left coronary artery was examined in rats. In the presence of large infarcts, ventricular failure developed two to three days after surgery, because of chamber dilation and thinning of the wall, resulting in an average 7.5-fold increase in diastolic stress on the surviving myocardium. Mural thinning of the ventricular wall remote from and bordering the infarction occurred through side-to-side slippage of myocytes and capillaries within the wall. Although an average hypertrophic growth of 22% of the spared myocytes has been found, this amount of hypertrophy was insufficient to restore normal myocardial function. Long-term cardiac restructuring after infarction was characterized by the persistence of chamber dilatation and thinning of the ventricular wall. In addition to the side-to-side slippage, lengthening of the myocytes was an important cause of ventricular changes. As the reactive hypertrophy of the unaffected ventricle was insufficient to re-establish the ratio of ventricular mass to chamber volume, the diastolic stress remained elevated and decompensated eccentric ventricular hypertrophy developed. The anatomical remodeling of the spared left ventricular myocardium is an important conditioning factor in the short- and long-term outcome of ischemic cardiomyopathy.