Depression is frequently seen in cardiac patients. It has been shown that depression often has a negative impact on the course of coronary disease. More recently, research has demonstrated that some antidepressants can be used safely to treat depressed coronary patients. Although the majority of patients improve substantially with antidepressant treatment, a significant proportion do not respond to antidepressants. This project seeks to better understand why depression does not improve equally well in all patients. Ultimately, the hope is to improve the treatments available to people affected by both cardiac disease and depression, and to help select the best type of treatment in advance for each individual based on his or her personal history, and biological characteristics.