To assess the presence of residual myocardial ischemia and its prognostic significance soon after an acute myocardial infarction (MI), right atrial pacing (RAP) was performed in 85 consecutive patients 1 day before hospital discharge. No patient was excluded from the study because of his clinical condition. The mean age of the patients was 61.2 years (range 29-85 years). The study was performed at the bedside 10-28 days (mean 14.2 days) after the MI. No complications occurred during or after the test. RAP was considered positive if 1 mm or more of horizontal St depression developed. The mean maximal pacing rate achieved was 147 beats/min (range 100-160 beats/min). There were 46 patients (54%) with negative and 39 patients (46%) with positive RAP. Of the 30 patients with anterior MI, 17% had positive RAP, compared with 61% of the 23 with inferior MI and 63% of the 32 patients with subendocardial MI. The average follow-up period was 5.8 months. Among the 46 patients with a negative RAP, there was one sudden death; no reinfarction occurred, but eight patients required cardiac hospitalization and five patients suffered chest pain. Among the 39 patients with a positive RAP, three died (one suddenly and two after reinfarction); four additional patients had reinfarction. There were 20 cardiac hospitalizations in this group. Eighteen patients suffered from chest pain. A treadmill test was performed 6 months after MI in 37 patients. Seventeen of the 21 patients with negative RAP had a negative test, whereas 13 of the 16 with positive RAP had a positive treadmill test 6 months later. We conclude that RAP can be performed safely in patients after MI. Forty-six percent of all post-MI patients had residual areas of stress-induced myocardial ischemia. RAP was sensitive in predicting subsequent reinfarction, cardiac death, cardiac rehospitalization, angina pectoris and the response to a treadmill test 6 months after MI.