The rate of cardiac deaths that are sudden is approximately 50%, and decreases with age. The causes of sudden cardiac death are diverse, and are a function of age. In children and adolescents, coronary anomalies, hypertrophic cardiomyopathy and myocarditis are frequent substrates for lethal arrhythmias; in adults, coronary atherosclerosis and acquired forms of cardiomyopathy are the most common findings at autopsies of sudden cardiac death. This review focuses on coronary causes of sudden cardiac death, especially congenital coronary artery anomalies, which result in sudden death almost exclusively in adults younger than age 35, and coronary thrombosis. The most lethal coronary artery anomaly is the left coronary artery arising from the right sinus of Valsalva; this anomaly often results in fatal arrhythmias, often with exercise. The right coronary artery arising from the left sinus of Valsalva may also be lethal in adolescents and young adults, but, unlike the anomalous left, is more often an incidental finding at autopsy. Approximately 60% of sudden coronary death is caused by coronary thrombosis, the rest die with severe coronary disease in the absence of thrombosis. The two major substrates of coronary thrombosis are plaque rupture and plaque erosion, and are not only different pathologically, but are seen in patients with divergent risk factor profiles. Plaque rupture is the most common cause of fatal coronary thrombus, and is characterized by necrotic core with a thin fibrous cap, infiltrated by macrophages. The factors that result in plaque instability and rupture are largely unknown, and are under intense scrutiny; morphologic studies have identified serum lipid abnormalities as a key risk factor in the development of plaque rupture. Plaque erosion, in contrast to plaque rupture, is seen in younger men and women, is not associated with lipid abnormalities, and does not result from exposure of the lipid core to the lumen. The heterogeneity of the atherosclerotic plaque and the diverse mechanics of plaque progression and thrombosis have only been relatively recently explored, and are largely elucidated by autopsy studies of victims of sudden coronary death.