Similar time course of ST depression during and after exercise in patients with coronary artery disease and syndrome X. To assess whether the time course of ST segment depression differs in patients with coronary artery disease and patients with angina and normal coronary arteries, the exercise tests of 54 patients with documented coronary artery disease and 25 patients with syndrome X (angina, positive exercise test, no evidence of coronary artery spasm, and normal coronary arteries) were compared. All tests were performed with therapy withheld, using the modified Bruce protocol. In each test, time, heart rate and blood pressure were measured at the onset and at 1 mm of ST segment depression, and at peak exercise. Recovery (return of the ST segment to baseline +/- 0.2 mm) time was also assessed. Peak ST segment depression was similar in coronary artery disease and syndrome X patients (1.5 +/- 0.3 versus 1.6 +/- 0.4 mm). In 42 coronary artery disease patients, ST segment depression developed early (less than or equal to 6 minutes) during exercise; this was associated with a short recovery (less than or equal to 3 minutes) in 17 (40%) and with a long recovery (greater than 3 minutes) in 25 (60%) patients. In 17 patients with syndrome X, ST segment depression developed early; it was associated with a short recovery in six (35%) and with a long recovery in 11 (65%) patients. Late (greater than 6 minutes) onset of ST segment depression was observed in 12 coronary artery disease patients; of these, eight (67%) had a short recovery and 4 (33%) had a long recovery. Late onset of ST segment depression occurred in eight patients with syndrome X; six (75%) had a short recovery and two (25%) had a long recovery. 