A morphometric echocardiographic analysis of left ventricular mass was performed in 110 heavy smokers and 110 controls aged 20-60. Taken as a whole, the smoker group revealed a higher ventricular mass index (88.4 +/- 19.5 v 78.3 +/- 16.8 g/sq m; p less than 0.01). The difference was not significant in the 20-40 age group (78.1 +/- 18.3 v 76.7 +/- 18.1 g/sq m) but was highly significant (p less than 0.001) in the 41-60 age group (96.0 +/- 18.8 v 80.7 +/- 15.8 g/sq m). The increase in mass may be related to increased catecholamine incretion, raised blood viscosity due to increased fibrinogen and haemocrite and to transitory but repeated increases in telesystolic stress caused by the cigarette smoke. The increase in myocardial mass together with other well-known coronary alterations induced by smoking might explain the greater incidence an severity of ischaemic heart disease, not to mention sudden death among heavy smokers.