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Heart pumping weakness occurs progressively in all patients with Duchenne muscular dystrophy (DMD), but symptoms only occur very late in the process. Regular imaging assessments of heart function are needed to see how the heart is ‘doing’ and how well it is responding to treatment with heart drugs. Echocardiography (echo) has been the standard type of imaging used for these assessments in the UK. It is widely available but has limitations. Cardiac MRI (CMR), although less readily available and more expensive, is better able to detect tissue changes in the heart before there is any reduction of heart pump function and retains accuracy in all measures even as DMD progresses. An expert panel of cardiologists, muscle specialists and patient representatives was set up to review evidence and provide expert guidance on how to use both echo and CMR best to the benefit of patients with DMD, Becker muscular dystrophy (BMD) and females affected by DMD-gene abnormalities (‘female gene carriers’).The working group concluded that echo should remain the predominant method used in heart checks for patients with DMD in the UK. However, wider use of CMR, performed at times individualised to key decision points after about the age of 10 years, would allow earlier detection of those heart changes prompting the introduction and changes in heart therapies. Similarly, greater use of CMR could contribute to improving cardiac management of males with BMD and females with DMD-gene variations._______________________Objective To provide guidance on the use of cardiac MRI (CMR) in the UK in paediatric and adult patients with Duchenne muscular dystrophy (DMD) or Becker muscular dystrophy (BMD) as well as recommendations for screening and monitoring females with dystrophin-gene variations. Specifically, to examine the ‘added value’ of CMR over echocardiography at selected time points in the assessment of individuals with or at risk of developing cardiac dystrophinopathy.Methods Initiated by an expert working group of UK-based and US-based imaging cardiologists, neuromuscular clinicians and DMD-patient representatives, draft guidelines were created based on published evidence, current practice and expert opinion. After wider consultation with UK cardiologists, consensus was reached on the optimal use of CMR in clinical decision-making about therapy.Results and conclusions Echocardiography should remain the predominant modality for cardiac surveillance and to guide therapy for patients with DMD in the UK. However, when tolerated, wider use of CMR at key stages in patients with DMD, older than age 10 years, and for males with BMD and females with DMD-gene variations would allow earlier detection of those with cardiac involvement and inform the earlier initiation of regimes of cardiac medications. In this way, greater use of CMR could contribute to improving cardiac health in each of these patient groups.