Progressive decrease in chest pain and surface ECG changes are commonly observed during successive balloon inflations in coronary angioplasty, which suggests a decrease in myocardial ischemic response. To assess this hypothesis, we continuously recorded intracoronary ECGs during four balloon inflations; each of the inflations was maintained to a minimum of 120 seconds in 19 patients who had significant stenosis in the left anterior descending artery and normal left ventricular function. Three successive QRS-T complexes were analyzed on surface and intracoronary ECGs for measurements of ST-segment elevation 60 milliseconds after the J point. Surface ECG changes were compared with intracoronary ECG changes. On intracoronary ECG, ST area (in square millimeters) and T wave amplitude (in millimeters) were also computed. Chest pain was noted as present or absent during each successive balloon inflation. Ability of intracoronary ECG to detect myocardial ischemia, which was defined as ST-segment elevation greater than 1 mm during balloon inflations 1 to 4, was 89%, 89%, 84%, and 74%, respectively and was higher than that of surface ECG, which was 68%, 63%, 68%, and 58%, respectively. On intracoronary ECG, when compared with the first balloon inflation, a significantly smaller increase in ST-segment elevation was noted during each subsequent balloon inflation, whereas a significantly smaller increase in ST area and T wave amplitude was noted only during balloon inflation 4. The number of patients who experienced chest pain decreased from 15 to 13, 10 and 6 from the first to the fourth balloon inflation. This report demonstrates a progressive decrease in myocardial ischemic response during successive and prolonged balloon occlusions.(ABSTRACT TRUNCATED AT 250 WORDS)