Major depression is a common comorbid condition in patients with coronary heart disease (CHD). Although mild emotional distress may be a normal reaction to myocardial infarction or other manifestations of CHD, major depression should not be considered a normal reaction, nor should it be ignored. Major depression is a debilitating comorbid disorder that can seriously complicate recovery and increase the risks of further cardiac morbidity and mortality. Fortunately, it is one that can be successfully treated in the majority of cases. The purpose of this review is to present the evidence for the negative prognostic effects of depression in cardiac patients and to discuss methods for assessing and treating depression in these patients.