Cardiac involvement is common in adult patients with the presence of HLA B27 with or without the HLA B27-associated spondyloarthropathy ankylosing spondylitis. Most patients with juvenile spondyloarthropathy, which begins at age 16 or younger, do not have spinal involvement and there are only few reports of cardiac involvement. This study sought to assess the prevalence of carditis in patients with HLA B27-associated juvenile arthritis (B27-JA). In a controlled study, 40 patients with B27-JA, among them only 1 with ankylosing spondylitis, were examined by electrocardiogram and echocardiography with pulsed and color-flow Doppler at rest and at the termination of a bicycle exercise and compared to an age- and sex-matched control group negative for HLA B27. Four patients with B27-JA, and none in the control group, had inflammatory aortic regurgitation. Late diastolic flow velocity was significantly increased in patients with B27-JA at the termination of exercise. HLA B27 is a risk factor for endo-/myocardial damage in patients with B27-JA, even in the presence of only short and mild articular disease. Patients with B27-JA should be screened for the presence of aortic regurgitation.