The relationships between structural alterations and left ventricular (LV) contraction abnormalities were studied in patients with coronary artery disease (CAD). Transmural biopsies of the LV anterior free wall were taken during aortocoronary bypass surgery (CABG) in 62 patients. When preoperative anterior wall motion (AWM) was reduced, significant myocardial cell degeneration was found in patients with as well as without previous anterior infarction (MI). The amount of myocardial fibrosis was increased only in patients with ECG evidence of previous anterior MI (p less than 0.001). In a second series of 139 CAD patients, cineventriculograms performed before and 8 months after CABG were examined. In patients with patent grafts to the LV anterior wall not previously infarcted, reduced AWM became normal. In patients with previous anterior MI the outcome of AWM was unpredictable (usually unimproved). Thus the histologic correlate of reduced AWM in segments not previously infarcted was progressive loss of contractile material in otherwise viable myocardial cells. Some reversibility was suggested by restoration of resting function after CABG. Unpredictable results in segments associated with pathologic Q waves appear related to the fibrous component of these previously infarcted areas.