The ventricular fibrillation threshold (VFT) was measured in 28 patients at the time of cardiac surgery. The VFT was measured with a 100 Hz train of 24 rectangular pulses positioned across the ST segment and T wave. Current was applied to the epicardial surface of either ventricle with a bipolar electrode probe. In six patients, the normal right VFT was 24.3 ± 5.2 mA, and in 10 patients the normal left VFT was 33.6 ± 9.5 mA (p < 0.05). In 12 patients with > 75% obstruction of the left anterior descending coronary artery, the left VFT was 18.6 ± 6.9 mA. This value was significantly less than the left VFT in patients without coronary artery disease (p < 0.001). This study shows that the VFT can be measured in man and that coronary artery disease reduces this parameter.