['The purpose of this study was to investigate the relationship between depression and heart rate variability in cardiac patients.', 'Heart rate variability was measured during 24-hour ambulatory electrocardiographic (ECG) monitoring in 40 medically stable out-patients with documented coronary heart disease meeting current diagnostic criteria for major depression, and 32 nondepressed, but otherwise comparable, patients. Patients discontinued beta-blockers and antidepressant medications at the time of study. Depressed patients were classified as mildly (n = 21) or moderately-to-severely depressed (n = 19) on the basis of Beck Depression Inventory scores.', 'There were no significant differences among the groups in age, gender, blood pressure, history of myocardial infarction, diabetes, or smoking. Heart rates were higher and nearly all indices of heart rate variability were significantly reduced in the moderately-to-severely versus the nondepressed group. Heart rates were also higher and mean values for heart rate variability lower in the mildly depressed group compared with the nondepressed group, but these differences did not attain statistical significance.'] Is severe depression associated with markedly reduced heart rate variability in patients with stable coronary heart disease?