Our purpose was to examine the cognitive processes that influence involvement in physical activity among 100 adolescents, 55 boys and 45 girls, ranging in age from 12 to 18 years, with trivial, mild, or moderate forms of congenital cardiac disease. We hypothesized, first, that the severity of the congenital cardiac malformation itself has an indirect effect on self-efficacy regarding physical activity, and that the relationship between the two is mediated by the recommendations of the cardiologist and the attitude of the mother. Second, we argued that self-efficacy serves as a mediating variable between the recommendations of the cardiologist and the attitude of the mother, on the one hand, and involvement in physical activity, on the other. The results confirmed both hypotheses. In a population of adolescents with trivial to moderate congenital cardiac malformations, beliefs in self-efficacy, rather than severity of the disease, were the most influential factors in determining whether or not adolescents will engage in sports or other physical activities. We also demonstrated the importance of the role played by the recommendations of the cardiologist in determining both the attitudes of the mother and the belief in self-efficacy of the adolescents.