The mouse cardiac truncated protein lacking the myosin protein binding domain (missing the 240 nucleotides at the 3' end) is under the control of the mouse alpha-myosin heavy chain promoter. The human myc epitope is placed after the initiator methionine residue. Western blot analysis indicates very little truncated protein in hearts while endogenous levels of Mybpc3 are unaffected. Multiple lines were established including 19, 24, and 133. All lines exhibit similar phenotypes and line 24 is entered as a representative line.