The cloning of a fourth mouse SCD gene, mSCD4, as well as its corresponding cDNA and amino acid sequences are disclosed. Mouse SCD4 is expressed mainly in the heart tissue and synthesizes the bulk of monounsaturated fatty acids in the heart. The disclosure here enables new tools (e.g., nucleic acids, polypeptides, antibodies, vectors, recombinant cells, and transgenic and knock-out animals) for studying the function of various SCD isoforms and their connection to various disease conditions. New tools for converting saturated fatty acyl-CoA to monounsaturated acyl-CoA and for identifying SCD modulators including isoform-specific modulators are also enabled. In addition, given that accumulation of lipid in the heart (fatty heart) can have deleterious consequences, the present invention also provides a new prevention and treatment target for fatty heart as well as methods for screening candidate drugs.