At least one quarter of all MIs are silent, without chest pain or other symptoms. These cases can be discovered later on electrocardiograms, using blood enzyme tests, or at autopsy without a prior history of related complaints. Estimates of the prevalence of silent MIs vary between 22 and 64%. A silent course is more common in the elderly, in people with diabetes mellitus and after heart transplantation, probably because the donor heart is not fully innervated by the nervous system of the recipient. In people with diabetes, differences in pain threshold, autonomic neuropathy, and psychological factors have been cited as possible explanations for the lack of symptoms.

What fraction of MIs are discovered with blood enzyme tests?