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Cigarette smoking increases the risk of myocardial infarction and sudden death (Ball and Turner 1974; Miettinen et al 1976; Rosengren et al 1988). Several mechanisms have been offered for this increased incidence. Cryer et al (1976) attributed the changes in blood pressure and heart rate with cigarett~ smoking to norepinephrine (NE) release fron, adrenergic nerves. NE release has also been shown to lower the ventricular fibrillation threshold (Verrier et al 1974, 1975). Thus, it is possible that the increased incidence of acute myocardial infarction and sudden death i,n smokers may be due to excessive sympathetic tone. It is also possible, however, that a decrease in parasympathetic tone, causing a relative excess of sympathetic tone, would create a similar condition. Given the high rate of cigarette smoking in psychiatric patients (Hughes et al 1986), it is important to determine the physiological effects of this addiction. Spectral analysis provides an estimate of the contribution of sympathetic and parasympathetic tone on heart rate variability (Hyndman and Gregory 1975; Rompelman 1977; Porges 1983). Therefore, the purpose of this