Certain clinical and morphologic observations are described in 4 men who had PTCA of the left anterior descending coronary artery early (4 hours) or late (80, 90 and 150 days) before sudden death. Histologically, each of the 4 patients had the site of PTCA narrowed 76 to 95% in cross-sectional area by atherosclerotic plaque. The early PTCA patient had coronary artery dissection at the site of PTCA. Each of the 3 late PTCA patients had a decrease in the mean transstenotic coronary gradient (17, 38 and 43 mm Hg) and an angiographic increase in the left anterior descending coronary artery luminal diameter (55, 60 and 65%) at the time of PTCA. At necropsy, 80, 90 and 150 days later, the LAD coronary artery in the area of the PTCA in each patient was narrowed 76 to 95% in cross-sectional area by plaques. No cracks in plaques or other lesions that may have resulted from PTCA were identified histologically in the left anterior descending coronary artery in any late PTCA patient.