To the Editor.
—The article by Hellerstein and Friedman "Sexual Activity and the Postcoronary Patient" (Arch Intern Med125:987-999, 1970) deserves comment regarding the inferences about the energy cost of sexual activity. To assess the oxygen cost of sexual activity, the authors have used the heart rate during sexual intercourse and compared it with the heart rate obtained during bicycle ergometer test conducted with the patient upright. Based on that, the authors were able to calculate that the oxygen cost of sexual activity corresponds to 60.3% of the maximal oxygen uptake as determined by ergometric tests. Moreover, the authors claim that the equivalent oxygen cost during sexual activity is less than that of a standard single Master two-step test.My objections to the use of these inferences to estimate oxygen consumption stems from the fact that one of the most important factors in determining the cardiovascular response to effort