Krittayaphong, R., Cascio, W. E., Light, K. C., Sheffield, D., Golden, R. N., Finkel, J. B., Glekas, G., Koch, G. G., & Sheps, D. S. (1997). Heart rate variability in patients with coronary artery disease: Differences in patients with higher and lower depression scores. Psychosomatic Medicine, 59(3), 231–235.