Cold weather and ischaemic heart disease.

It is well known that the incidence of ischaemic heart disease tends to be higher in winter than in summer. In England and Wales, for example, mortality from "arteriosclerotic heart disease" (ASHD :ISC 420) averages 50 per cent. more in midwinter than in mid-summer (Annual Reports of the Registrar General of England and Wales); and a similar swing has been reported for hospital ad- mission rates It may how- ever be objected that results of this kind could have been biased by diagnostic uncertainties, by competing causes of morbidity and mortality, and by the possi- bility that respiratory infections may cause increased illness or death in persons already suffering from heart disease.