Decreased heart rate (HR) variability is an independent risk factor for mortality in cardiac populations. Clinical depression has also been associated with adverse outcomes in patients with coronary artery disease (CAD). This study tests the hypothesis that depressed patients with CAD have decreased HR variability compared with nondepressed CAD patients. Nineteen patients with angiographically documented CAD and either major or minor depression were compared with a sample of nondepressed CAD patients according to age, sex, and smoking status. All patients underwent 24-hour Holter monitoring, and the standard deviation of all normal-to-normal intervals was used as the primary index of HR variability. HR variability was significantly lower in depressed than nondepressed patients (90 +/- 35 vs 117 +/- 26 ms; p < or = 0.01), even after adjusting for relevant covariates. Thus, decreased HR variability may help explain the increased risk for cardiac mortality and morbidity in depressed CAD patients.