The effects of passive smoking on ischemic heart disease are reviewed. Short-term exposures of 20 min to 8 h result in increased platelet sensitivity and decreased ability of the heart to receive and process oxygen. Longer term exposure results in plaque buildup and adverse effects on blood cholesterol. The available epidemiology is reviewed, and it is concluded that passive smoking increases the coronary death rate among U.S. never smokers by 20% to 70%. The newest Environmental Protection Agency procedures for estimating deaths from passive smoking, when applied to the epidemiologic results on heart disease and passive smoking, indicate that in 1985 an estimated 62,000 ischemic heart disease deaths in the United States were associated with exposure to environmental tobacco smoke. Clinicians are advised to counsel their patients to avoid tobacco smoke at home, at work and in transportation settings.