Depression is common in patients with physical illness. The National Center of Neurology and Psychiatry has launched a joint project with five other centers in Japan, aiming at improving the quality of mental care in patients with physical illness. In the present overview focusing on heart disease, we review the prevalence of depression in patients with heart disease, the impact of depression on cardiac prognosis, the possible mechanisms of depression in patients with heart disease, drug-drug interactions between cardiac and psychotropic agents and the possible therapeutic approaches to treating these patients. Depression and heart disease often coexist and each can lead to the other. Various biological and behavioral mechanisms have been proposed to explain an association between heart disease and depression, including autonomic nervous system activity, impairment of platelet function, endothelial dysfunction, inflammatory changes, and health-related behaviors. Combination therapy with tricyclic antidepressant and cardiac agents must be approached with caution to avoid drug-drug interactions. Selective serotonin reuptake inhibitors (SSRIs) are the first line treatment for patients with heart disease and moderate to severe depression. Although no single intervention has been established as the standardized treatment, recent studies suggest that collaborative care improves both depressive symptoms and cardiac outcomes, and that patient's participation is a key to successful treatment. Bridging the gap between cardiology and psychiatry is essential, and psychiatrists can play a vital role in taking care of the mental health of patients with heart disease.