Still's disease is a subset of juvenile idiopathic arthritis (JIA) that usually presents with intermittent fever, rash, and arthritis. Extra-articular flares can occur several years after disease onset. We report two cases of adult Still's disease with myocarditis after several years of being in remission. A 34-year-old Caucasian man with history of systemic juvenile arthritis in remission since age 13 was admitted in hospital with 10 days history of fever, odynophagia, and arthralgias. Chest X-ray and cardiac ultrasound showed cardiac enlargement. An endomyocardial biopsy revealed acute myocarditis. He was treated with methylprednisolone and intravenous gammaglobulin, with improvement of his general condition and cardiac parameters. A 16-year-old Caucasian male patient with history of systemic JIA in remission for the last 7 years was admitted with 7 days history of fever, odynophagia, arthralgias, and myalgias. Two days after admission, he developed chest pain and pericardial rubbing was found on examination. Cardiac ultrasound showed left ventricular dilatation with impaired systolic function, and posterior, inferior and apical-septal wall hypokinesia. Blood test showed elevated creatine phosphokinase levels. He was treated with IV methylprednisolone with normal follow-up cardiac ultrasound. Cardiac involvement in patients with systemic JIA can be the first symptom of disease reactivation, even after many years of disease remission.