Background This study compared the effect of 5 recumbent positions on cardiac autonomic nervous modulation in patients with coronary artery disease (CAD). Methods and Results Spectral heart rate variability analysis was performed on 33 CAD patients and 17 patients with patent coronary arteries in random order in 5 positions; namely, supine, right lateral decubitus, left lateral decubitus, left prone and right prone positions. In the right lateral decubitus position, the vagal modulation was the highest and the sympathetic modulation was the lowest among the 5 recumbent positions in the control group. In the CAD patients, the vagal modulation in the supine position was significantly lower than that in the other 4 positions. The lower the normalized high-frequency power (nHFP) in the supine position, the larger the percent age increase in nHFP when the position was changed from supine to another recumbent position in both CAD patients and controls. There was no significant change in the respiratory rate when the position was changed from supine to any of the other 4 positions. Conclusions Right lateral decubitus position leads to the highest vagal modulation in the controls, whereas the supine position leads to the lowest vagal modulation in the CAD patients. In addition to the right lateral decubitus position, both the right and left prone positions can be used as a vagal enhancer in patients with CAD as compared with supine, especially for those patients who have severely reduced cardiac vagal modulation while supine. (Circ J 2008; 72: 902 - 908)