The relationship between passive smoking and the risk of cardiovascular disease was reviewed and discussed. Epidemiologic evidence, suggesting that passive smoking at home is related to heart disease in never smokers, has been accumulating. Nine epidemiological studies have evaluated the relative risk (RR) for heart disease in never smokers living with current or former smokers relative to never smokers living with nonsmokers. RRs ranging from controlled for confounding by cardiovascular risk factors such as cholesterol, blood pressure, and obesity showed RRs ranging from 1.59 to 2.01. The major weakness in the studies was the indirect methods used for assessing passive smoking exposure and the lack of data on environmental tobacco smoke (ETS) exposures outside the home. Clinical and laboratory animal studies have indicated that ETS can increase blood carboxyhemoglobin concentration, increase platelet aggregation, impair platelet function, damage the arterial endothelium, lower high density lipoprotein cholesterol concentration, and increase fibrinogen concentration. An assessment of the risk of ischemic heart disease (IHD) resulting from ETS exposure was performed. It was assumed that 35,000 to 40,000 deaths from IHD attributable to ETS occurred annually in the US among never and former smokers. The lifetime risk of a male never smoker living with a current or former smoker dying from IHD by the age of 74 years as a result of ETS was estimated to be 9.6%. The lifetime risk for a male never smoker living with a nonsmoker was 7.4%. The corresponding risks for female never smokers were 6.1 and 4.9%. The author concludes that if the existing epidemiological data are valid ETS associated cardiovascular disease mortality constitutes a more serious public health problem than ETS associated lung cancer.