In order to properly advise cardiac patients in the regulation of their sexual activity, more basic physiologic information is needed concerning the cardiovascular effects of sexual intercourse. This study examined the effects of the male's position during sexual intercourse on heart rate and blood pressure responses. Eight men, 24 to 40 years of age, were studied in the privacy of the bedroom during sexual activity with their wives. The ECG was monitored continuously by portable tape recorder and the arm blood pressure (BP) was measured intermittently with an automatically inflated cuff and ultrasonic detector device controlled by the subject. A total of 35 episodes of sexual intercourse were monitored; 16 were with the male-on-top (MOT) and 19 were in the male-on-bottom (MOB) position. The mean maximal heart rate (HR) for MOT at orgasm was 114 compared to 117 in the MOB position, representing 61 per cent of predicted maximal HR for men in the 20 to 29 age group. Mean BP at orgasm in the MOT was 163/81 and 161/77 in the MOB position. The differences in mean HR, BP, and pressure rate product (PRP) were not statistically significant with regard to position at rest intromission, orgasm, or during the recovery period. This study indicates no difference in the heart rate and BP responses of the male during sexual intercourse in two different positions. There is, therefore, no physiologic basis for advising cardiac patients to utilize the MOB position during sexual intercourse.