Twenty-four hour Holter ambulatory electrocardiographic recordings were obtained before and after successful coronary angioplasty in 36 patients. Twenty-five patients had one vessel, 10 had two vessel and 1 had three vessel coronary artery disease. Holter monitor-detected myocardial ischemia, defined as ST segment depression or elevation greater than or equal to 1 mm, was present in 10 patients (28%). These 10 patients had a total of 39 ischemic episodes of 3 to 144 minutes' duration, with a total cumulative duration of 398 minutes. None of the 10 had Holter monitor-detected ischemia after successful angioplasty (p less than 0.01). Treadmill exercise duration increased by 29% after coronary angioplasty (p less than 0.01), and peak exercise heart rate-systolic blood pressure product increased by 27% (p less than 0.01). Thus, Holter monitor-detected myocardial ischemia is a relatively uncommon finding in patients with predominant single vessel coronary artery disease undergoing coronary angioplasty. When such ischemia is present, it is eliminated by successful coronary angioplasty.