Exposure to cold causes a vasoconstriction and a tachycardia, both resulting in a rise of blood pressure and cardiac work. This last effect may have a deleterious influence on people suffering from ischaemic heart disease (IHD). Moreover, coronary artery spasm could occur if vasoconstriction extends to the heart vessels. Epidemiologic studies have shown that mortality from IHD was correlated to the ambient temperature. There will be more deaths per day in the winter, and fewer in the summer. However, the daily number of deaths also increases during the heat waves. During a cold test, the coronary blood flow remains normal or slightly increased in normal subject. There is never a coronary artery spasm. Subjects who suffer from angina but have normal coronary arteries behave in the same way as normal subjects. Patients with IHD show a decrease in coronary blood flow. In a few cases, those patients may exhibit a coronary spasm with chest pain and even myocardial infarction. It is concluded that people with normal cardiovascular function are unaffected by cold stress whereas those with IHD may be crippled, although rarely, by exposure to cold, especially if they perform a physical work.