The purpose of this study was to evaluate the in vivo characteristics of coronary atherosclerosis by using high frequency epicardial echocardiography. High frequency epicardial echocardiography was used to evaluate residual lumen and wall morphology at the sites of maximal coronary atherosclerosis in 26 patients undergoing coronary artery bypass grafting. The maximal/minimal wall thickness ratio was 3.1 +/- 0.2 (mean +/- SEM) with a large range (1.3 to 7.5). Portions of the wall were normal in 16 of 31 lesions; the percent normal circumference ranged from 9% to 85%. Maximal/minimal lumen diameter ratio was 1.5 +/- 0.1 (range 1.1 to 2.9). The shape of the residual coronary lumen was noncircular in 16 lesions: oval in 13 and complex in 3. The residual coronary lumen was eccentrically placed within six arteries. These data emphasize the variability of residual lumen and wall geometry in atherosclerosis.