There is a national concern about the lack of participation in physical activity by adolescent females. This study shows, that in a period of seven weeks, there were no significant differences in resting heart rate scores for three groups of adolescent girls, ages 14-15 years, who participated in moderate (60-70% of their maximum heart rate) physical activity for 20 minutes during their physical education class. The reason for no significant change in resting heart rate could be due to the duration of the study. This study was intended to be 12 weeks long (Stanten, 1998). However, due to delay in the calibration of the heart rate monitors and to school holiday vacation at the end of the study, it had to be shortened. Although there were nonsignificant differences in resting heart rate from pretest to posttest, the study showed that being encouraged to exercise at 60– 70% of one''s maximum heart rate for 7 weeks can positively affect the resting heart rate for some and have no affect on others. From this study insightful information was gained that could assist future researchers.