The effects of smoking on the signal-averaged electrocardiogram in normal subjects. Tobacco smoking increases the risk of sudden cardiac death, possibly by altering the substrate for propagation or sustainment of ventricular tachyarrhythmias. To test this hypothesis, 15 long-term smokers without known coronary artery disease abstained from tobacco smoking for 12 h, after which they underwent SAECG before, 15 min after and 30 min after smoking two cigarettes. Other than minor lengthening of filtered QRS duration, no significant change in time-domain SAECG parameters was noted. We conclude that late potentials are not produced by cigarette smoking and that ventricular arrhythmia substrate as measured by SAECG variables is not worsened in long-term smokers without evidence of coronary artery disease. 