Patients engaged in significantly more mild and total exercise during summer vacation than they did during the fall semester. They also engaged in significantly less vigorous exercise during summer vacation than they did in the fall semester. Female respondents engaged in significantly less moderate (P = .019), vigorous (P < .001), and total (P = .015) exercise than did their male counterparts but showed no difference in mild exercise. During the summer and fall, nearly 50% of the adolescents followed their cardiologist's recommendations for exercise. Adolescents with mild CHD engaged in more exercise during summer vacation but engaged in more vigorous exercise during the fall semester. Approximately one half did not follow the exercise intensity recommended by cardiologists. Inadequate exercise patterns may lead to cardiovascular complications. Planned interventions related to exercise instruction are needed for adolescents with CHD.