Low heart rate variability is a marker of increased risk of cardiac mortality, and is observed in depressed coronary artery disease patients. Some antidepressants may themselves, however, decrease heart rate variability. We will test the hypothesis that greater reduction in heart rate variability will be associated with duloxetine (which has noradrenergic activity) than escitalopram (a selective serotonin reuptake inhibitor). We will also test the hypothesis that changes in heart rate variability are related to the magnitude of norepinephrine transporter occupancy.