Dr. Sheps and colleagues assessed the effect of exposure to carbon monoxide (CO) on ventricular arrhythmias in 41 nonsmoking human volunteers with coronary artery disease. On 3 consecutive days, volunteers were exposed in random order to air, 100 ppm CO (target 4% carboxyhemoglobin), and 200 ppm CO (target 6% carboxyhemoglobin), followed by a bicycle exercise test. Radionuclide cardiac ventriculography and ambulatory electrocardiogram were performed at rest and during exercise.