Left ventricular function during exercise and recovery was investigated in patients with angina pectoris, ST segment depression during exercise and angiographically normal coronary arteries (syndrome X) using a continuous left ventricular function monitor with cadmium telluride detector (CdTe-VEST). Fourteen patients with syndrome X and 14 patients with atypical chest pain without ST segment depression during exercise and normal coronary arteries (control group) performed supine ergometric exercise after administration of 740-925 MBq of technetium-99m labelled red blood cells, and left ventricular function was monitored every 20 s using CdTe-VEST. Left ventricular ejection fraction (EF) response was impaired (_<5% increase from rest to peak exercise) in 11 or 14 patients with syndrome X but in none of the control patients. Resting EF was similar in the two groups (62.1%+6.7% in patients with syndrome X, 61.9%+6.2% in controls); however, EF increase from rest to peak exercise was lower in syndrome X (-3.1+9.5% vs 14.7%+7.4%, P <0.001). After cessation of exercise, all patients showed rapid EF increase over baseline and this EF overshoot was lower (19.3%+8.3% vs 26.4%+7.3%, P <0.001) with the time to EF overshoot longer (114+43 s vs 74+43 s, P<0.05) in patients with syndrome X. Thus, in patients with syndrome X, left ventricular dysfunction was frequently observed during exercise in spite of normal epicardial coronary arteries.