The present invention relates to cardiac performance, in particular to regulating cardiac performance via recombinant troponin I (TnI) protein and nucleic acids encoding recombinant TnI. The present invention provides nucleic acids encoding gain of function TnI proteins (e.g., cTnlA164H), vectors containing such nucleic acids, host cells containing such vectors, transgenic animals carrying a gain of function TnI protein (e.g., a cTnlA164H transgene), and therapeutic agents (e.g., comprising recombinant TnI, TnI analogues, synthetic TnI, or the like) or agents for gene therapy of heart failure or disease for research and therapeutic uses.