Patients with coronary artery disease (CAD) have depressed vagal modulation. Because the mortality risk from acute myocardial infarction is lower in patients with higher vagal modulation, methods that can increase vagal modulation are desirable for patients with CAD. The right lateral decubitus position has been found, in young healthy subjects, to lead to the highest vagal modulation among 3 recumbent positions using spectral heart rate variability (HRV) analysis. This study investigated which recumbent position can give rise to the highest vagal modulation in patients with severe CAD. Twenty-seven patients scheduled for coronary artery bypass graft surgery and 17 patients with angiographically normal coronary arteries were studied. Spectral HRV analysis was performed in random order on these patients in 3 recumbent positions: namely, the supine, left lateral decubitus, and right lateral decubitus positions. Normalized high-frequency power was the highest, whereas normalized low-frequency power and low/high-frequency power ratio in the right lateral decubitus position were the lowest, among the 3 recumbent positions in both groups of patients. The lower the normalized high-frequency power in the supine or left lateral decubitus position, the higher the increase in the normalized high-frequency power when the position was changed from supine or left lateral decubitus to right lateral decubitus in patients with severe CAD. Right lateral decubitus position can lead to the highest vagal modulation and the lowest sympathetic modulation among the 3 recumbent positions in patients with severe CAD. Therefore, the right lateral decubitus position can be used as an effective physiologic vagal enhancer in patients with severe CAD.