In this study 140 patients who have had a recent hospitalization for an acute coronary syndrome and who have major depression will all receive 12 weeks of treatment with the antidepressant citalopram and regular clinical management visits from a mental health professional. The objective is to examine the characteristics of depressed cardiac patients who do and do not show an improvement in depression with citalopram treatment. There is evidence that the causes of depression may be different in some people with cardiac disease than in individuals who do not have heart problems, and these differences may be at least partially involved in determining response to antidepressant treatment. Inflammation, one of the body's responses to the development of atherosclerosis (hardening of the arteries and blockages in the heart) may be particularly important in producing depression in cardiac patients. There may also be changes in the body's metabolism of tryptophan, a protein that is involved in making serotonin, and levels of serotonin are often low in depression. Other factors thought to influence the development of depression include childhood experiences and personality factors. Heredity and family history also seem to play a role in some people with depression and heart disease. Finally, some patients experience sleep apnea, interruptions in breathing while they are asleep, that can contribute to both cardiac disease and depression.