In the heart, muscarinic M2 receptor is the typical functional subtype, we observed that intravenous injection of nonselective muscarinic acetylcholine receptor agonist (oxotremorine, 0.2 mg/kg/day for 4 weeks) via the tail vein in CHF rats exerted protective effects in the heart, however, application of selective muscarinic M2 receptor antagonist (methoctramine, 0.5 mg/kg/day for 4 weeks) via tail intravenous injection in CHF rats had no significant effects on cardiac performance (Supplementary Figure S2). This evidence concerns the gene CHRM2 and congestive heart failure.