The effects of glucose-insulin-potassium infusion (GIK) on atrial pacing-induced angina, ST depression, abnormal left ventricular end-diastolic pressure during pacing interruption (LVEDPi) and lactate metabolism (L), were studied in 18 patients: ten had angina during pacing = Ischemic group, and eight (5 normals and 3 with coronary artery disease) remained asymptomatic = Nonischemic group. The study consisted of 8-10 minute periods of control, pacing and recovery, before and after GIK. No untoward effects were observed. Comparison of the pacing responses (GIK vs pre-GIK states) showed that during GIK, angina occurred in only 4 patients, while significantly less severe changes were observed in ST depression (1.4 +/-0.5 vs 2.4 +/- 0.4 mm) and LVEDPi (16 +/- 3 vs 23 +/- 3 mm Hg). Lactate extraction was also higher (8.1 +/- 10.9 vs -5.2 +/- 11.1%), but not significantly so, although L became normal in 4 subjects and improved in another. These results indicate that GIK infusion was well tolerated and had a beneficial effect on pacing-induced myocardial ischemia.