Myocardial metabolism was studied during rapid atrial pacing in 22 patients with angina and angiographically normal coronary arteries. Pyruvate, non esterified fatty acid and lactate levels were measured in the coronary arteries and veins under basal conditions, at the peak of atrial pacing and during the recovery phase. A control group of 8 patients had neither angina, ST depression, or lactate production during atrial pacing. A correlation was observed between the coronary arterio-venous difference and arterial pyruvate and non esterified fatty acid levels in the 22 patients during the 3 periods of study. The control patients did not differ significantly from the rest of the population. There was a correlation between the coronary arterio-venous difference and arterial lactate levels under basal conditions in all of the study and control groups. This correlation remained significant during atrial pacing and the recovery period only in the control group. It was possible to distinguish a group of 14 patients (64 p. 100) (Group A) with a correlation coefficient of lactate production similar to the control group (+/- 2 standard deviations) during atrial pacing, from a second group of 8 patients (36 p. 100) (Group B) with abnormal myocardial metabolism. The arterial lactate concentrations were similar in both groups in the 3 periods of study. A coefficient of lactate extraction less than 10 p. 100 was observed in 2 patients in Group A and in 7 patients in Group B (88 p. 100, p less than 0.01). One patient in Group B had a coefficient of lactate extraction greater than 10 p. 100 (+ 13 p. 100).(ABSTRACT TRUNCATED AT 250 WORDS)