The common cause of sudden cardiac death is ischaemic heart disease. Such patients may have an occlusive recent thrombosis in a major coronary artery but the largest group has no recent occlusion. Comparison of such patients without occlusion with non-cardiac death control hearts suggests that an area of stenosis of 85 per cent is the best discriminating level. Most subjects who die of ischaemic heart disease suddenly have this degree of stenosis in two or three major arteries. Non-ischaemic sudden cardiac death occurs in hypertrophic obstructive cardiomyopathy and in severe left ventricular hypertrophy particularly from aortic valve stenosis. When the heart is macroscopically normal, review of previous electrocardiograms is the most helpful guide and may disclose conditions such as a long QT interval or pre-excitation. When no such data are available examination of the conduction system histologically may be helpful but is often non-specific. Use of the term "cardiomyopathy" by pathologists to cover all non-ischaemic sudden cardiac death is clinically misleading.