The present invention provides methods for screening drugs inhibiting the expression of OSF-2 gene or the production or function of the protein encoded thereby and therapeutic agents for heart failure having such effects. Useful methods for diagnosing heart failure can be provided by monitoring the expression or variation of said gene or the production of the protein encoded thereby. The present invention also provides transgenic animals with forced expression of OSF-2 gene and methods for studying changes in gene expression or protein production or the functions of various genes or proteins with the progress of the pathology of heart failure using them and novel therapeutic agents for heart failure.