DMD and cardiomyopathy: Heterozygous mdx mice (expressing dystrophin in the heart at the level of ~50%) experience only mild cardiomyopathy,16 and cardiac muscle exhibits minor functional improvements with even as little as ~3% dystrophin expression.17 Further studies from our group suggest that therapeutic re‐introduction of ~15% of normal dystrophin in adult mdx mice is sufficient to provide protection against contractile damage.18