A large series of epidemiological, clinical and pathological studies relate cigarette smoking to the development of cardiac damage. Data of our studies on both active and passive smoking show the following results. (A) Active smoking: (i) clinical and electrocardiographic signs of myocardial ischaemia were seen in 266 (38%) out of 700 smokers vs 25 (12.5%) out of 200 non-smokers (p < 0.01) with similar characteristics, (ii) a significantly higher incidence (p < 0.05) of reinfarctions in 443 smokers who continued to smoke (200 reinfarctions, 45%) compared to 724 subjects with a previous infarction who stopped smoking (289 reinfarctions, 40%), (iii) a significantly higher incidence of reinfarction in smokers with a previous myocardial infarction who smoked more than 15 cigarettes per day compared to a similar population who smoked less than 15 cigarettes per day (118/212, 56% vs 82/231, 35%). (B) Passive smoking: 19 male volunteers (9 healthy and 10 with a previous myocardial infarction), who did not smoke, underwent exercise stress testing twice; once in a smoke-free environment and once in a smoking environment. Cardiac performance of these subjects was impaired significantly in the smoking environment. Pathologically, severe coronary alterations, especially in users of oral contraceptives, massive myocardial infarctions and focal myocardial lesions were seen. Several variables such as type of smoking, subject and environment may interfere with experimental results. When we standardise these variables, cardiac damage caused by cigarette smoking is an undoubted fact.