Platelets, the smallest corpuscular component of human blood, are central to various crucial biologic pathways in the human body. Diminished platelet function is thought to contribute to the increased risk of ischemic heart disease in patients with major depressive disorder, and to the increased morbidity and diminished survival of depressed patients after an index myocardial infarction. We reviewed both recent studies that evaluated platelet function in various patient groups and recent information regarding the potential beneficial effects of selective serotonin reuptake inhibitors on platelet reactivity.