The aim of this prospective noninvasive follow-up study was (1) to assess the progression of cardiac involvement (CI) in patients with myotonic dystrophy (MD), Becker’s muscular dystrophy (BMD) and mitochondrial myopathy (MMP), (2) to find out if CI and neurologic impairment are related and (3) to determine how often cardiac investigations should be performed. Clinical, electrocardiographic, echocardiographic and 24-hour ambulatory electrocardiographic examinations were performed at yearly intervals. CI was assessed qualitatively by the presence of pathologic examinations and quantitatively by the number of pathologic examinations. Qualitatively, CI was present at baseline in 36 of the 38 cases (18–68 years) and the number of cases did not change. Quantitatively, CI progressed after 1 (2) year in 50% (50%) of patients with MD (n = 16), 0% (43%) of patients with BMD (n = 7) and 27% (27%) of patients with MMP (n = 15). CI and neurologic impairment were not related (p = 0.54). Cardiac investigations should be repeated at yearly intervals irrespective of whether there is neurologic deterioration or not.