Nucleic acids encoding modified myosin heavy-chain-associated RNA transcripts are provided. The modified myosin heavy-chain-associated RNA transcripts belongs to a cluster of long noncoding RNAs (lncRNA) and bind to chromatin remodeler Brg1 to inhibit Brg1's genomic targeting and gene regulation function. The modified myosin heavy-chain-associated RNA transcripts expressed in an individual inhibit Brg1's gene regulation function and protect the heart of the individual from myopathy and failure. One of the modified heavy-chain-associated RNAs is a 400 base pair fragment segmented from a natural 779 base pair sequence of Mhrt (Mhrt779) and has the same cardioprotective effects as the Mhrt779.