Depression is an independent risk factor for morbidity and mortality in patients with coronary artery disease (CAD). Altered autonomic nervous system (ANS) activity, a common feature of depression, is also a risk factor for cardiac events in patients with CAD. Heart rate variability (HRV) reflects ANS activity, and reduced HRV predicts morbidity in cardiac populations. The purpose of this study was to determine whether differences in HRV exist between depressed and nondepressed patients with CAD. Twenty-one depressed inpatients, with angiographically documented CAD were retrospectively matched to 21 nondepressed CAD patients by sex, age, and smoking status. Demographic, medical, psychological interview data, and 24-hour ECG recordings were obtained. Depressed subjects had significantly lower HRV, or trends toward lower HRV, than nondepressed subjects, even after controlling for severity of CAD. Subject groups did not differ on left ventricular ejection fraction, history of myocardial infarction, or any other relevant medical variable assessed. These results suggest that depression is associated with decreased HRV in patients with CAD, and may help to explain the increased rates of cardiac events observed in CAD patients with depression.