The present invention relates to methods of identifying whether a candidate compound is a modulator of a G protein-coupled receptor (GPCR). In some embodiments, the GPCR is mammalian, preferably human. In some embodiments, the GPCR is expressed endogenously by cardiomyocytes. In some embodiments, the GPCR is coupled to Gq. In some embodiments, the GPCR increases the intracellular level of inositol 1,4,5-triphosphate (IP3). In some embodiments, a modulator of the GPCR is a modulator of cardiomyocyte hypertrophy. The present invention further relates to methods of using a modulator of the GPCR. Preferred modulators are inverse agonists and antagonists. Inverse agonists and antagonists of the invention are useful as therapeutic agents for the prevention or treatment of heart disease, including hypertrophic cardiomyopathy and congestive heart failure, in particular hypertrophic cardiomyopathy resulting from post-myocardial infarction remodeling, cardiac valve disease, sustained cardiac afterload, myocarditis, and familial hypertrophic cardiomyopathy.