Regular physical activity prevents chronic disease and moderate to vigorous participation provides additional health benefits. Therefore, adolescents with congenital heart disease risk developing latent diseases due to real or perceived physical activity restrictions. Habitual physical activity levels, psychological determinants and advice received were examined by postal survey of 434 West Australian adolescents aged 12-18 years with congenital heart disease. Survey results (n = 153) were compared with published normative adolescent data. Total activity was classified as vigorous, adequate or inadequate according to metabolic equivalents, reported frequency and duration. Comparable numbers of respondents and healthy peers were active (winter 62% vs 74%; and summer 73% vs 82% respectively, p = 0.27). However, significantly fewer male respondents were classified as vigorously active compared with healthy peers, in both winter (48% vs 67%, p < 0.02), and summer (48% vs 69%, p = 0.04). Similar, but non-significant, trends were found when comparing female respondents with healthy peers and for mild versus severe disease groups. Self-efficacy ratings did not explain differences in physical activity intensity. Congenital heart disease may impact on the intensity of physical activity undertaken by affected adolescents thus denying additional health benefits. Physiotherapists could facilitate these adolescents to achieve more moderate to vigorous physical activity, to offset adult sedentary behaviour.