Prompted by a clinical observation of an increase in hospital admissions for acute myocardial infarction during an influenza outbreak, a study was designed to examine the number of deaths from ischaemic heart disease (IHD) at the time of influenza. Deaths from IHD were found to be increased at all ages, and particularly in younger age groups when deaths attributed specifically to acute myocardial infarction are considered. The question of whether influenza could act as a precipitating factor in acute myocardial infarction is discussed, together with a possible mechanism.