Transient ischemic episodes at rest in patients with coronary artery disease have been attributed to mental stress. The means to monitor and record cardiac function changes due to mental stress is now available by utilizing the nuclear VEST.Eight, patients with angiographically documented coronary artery disease and 8 normal volunteers underwent a 4 hour session of continuous monitoring and recording of the left ventricular function, electrocardiogram, and blood pressure during exercise and mental stress. In the normal group, all subjects showed the expected normal response to exercise with an increase in ejection fraction, heart rate and blood pressure. During mental stress two subjects (25%) showed transient episodes of ejection fraction decrease that were not associated with chest pain, ST changes or significant changes in blood pressure. In the group of coronary artery disease patients, five (63%) had an ischemic response to exercise by electrocardiographic and radionuclide ventriculography criteria with evidence of chest pain in three of them. All of them revealed transient episodes of left ventricular dysfunction during mental stress. Episodes were painless, occurred at low heart rate and in most cases were accompanied by ST-segment changes. The rest of the patients with a normal response to exercise showed slight changes of the ejection fraction above the baseline.The results provide evidence that there is marked disparity in the incidence of chest pain and ST-segment changes, despite similar ischemic ejection fraction response between mental and physical stress. This is indicative of a major role of mental stress in provoking silent ischemia that potentially might provide additional clinical information compared to exercise test.