A rat myosin heavy chain promoter drives the expression of a rat cardiac alpha myosin heavy chain (Myh6) cDNA that was modified by mutating residue 1445 from a G to an A, and the deletion of codons 468-527. This resulted in a R403G substitution and a deletion in the putative actin binding domain in the encoded protein. This transgenic line exhibits a strong phenotype. (J:36522)