Using Elisa for cAMP, immunohistochemistry for α-SMA and FSP-1, Western blotting, and qPCR for protein and mRNA expression of the cAMP/Rap1A signaling pathway and myocardial fibrosis effector, we found that ONSMP effectively up-regulated the cAMP content in rat myocardial tissues, decreased the α-SMA and FSP-1 positive expression, promoted the protein and mRNA expression of β1-AR, AC6, and Epac1, decreased the protein and mRNA expression of CCND1, α-SMA, FSP-1, COL I, and COL III, promoted the activation of Rap1A, and inhibited the activity of STAT3. This evidence concerns the gene RAPGEF3 and Myocardial fibrosis.