Bisoprolol in DMD Early Cardiomyopathy

Inclusion Criteria: * Older than(including) 7 years old * A definite diagnosis of DMD with muscle pathology confirming the expression of dystrophin lower than 5% and/or confirmed mutations in the DMD gene using a clinical accepted technique that completely defines the mutation. * Using ACEI or ARB for more than 1 month * Confirmed myocardial damage in one or more left ventricular segments evident by late gadolinium enhancement and preserved left ventricular systolic function(\>45%) by cine cardiac MR in 45 days * Normal renal function * Holter and blood pressure shows no contraindication of using bisoprolol Exclusion Criteria: * Having metal implanted in body * Having claustrophobia * Allergic to gadolinium * Complicated with other cardiovascular diseases * Medical history or Holter show bradyarrhythmia like II/III degree atrioventricular block, sick sinus syndrome etc. * Systolic blood pressure lower than 90mmHg or rest heart rate lower than 75bpm * Having COPD or asthma history * Having other complications: tumor, endocrine diseases * Having beta blockers therapy * Planned operation in the future 12 months * Allergic to bisoprolol