Over several decades, a large body of evidence has emerged to suggest that depressive disorder is a risk factor for heart diseases, both aetiologically and prognostically. Several large, prospective, longitudinal studies have examined the relationship between depression and the development of coronary artery disease (CAD); they reveal that the relationship is significant and independent of conventional risk factors. Prognostic studies have shown that depression is associated with two to three times higher mortality after myocardial infarction, unstable angina or coronary artery bypass grafting, and in patients with stable CAD compared with such patients without depression. Depression also has been found to increase mortality and morbidity in patients with heart failure, regardless of its aetiology. Such adverse associations persist after adjustment for conventional prognostic risk factors.Despite all of these findings, depressed patients with heart disease are less likely to be recognised clinically as being depressed than those patients who have depression but no heart disease. The very limited evidence available from pharmacological clinical trials raises concern about the safety of antidepressants in CAD and heart failure. In addition, no research has addressed whether the treatment of depression in patients with heart disease will improve their prognosis.