ERBB agonist-1 (Compound EF-1) is an ERBB4 agonist that activates the ERBB4 signaling pathway by inducing ERBB4 receptor dimerization, with an EC50 of 10.5 μM. It promotes phosphorylation of Akt and ERK1/2, reduces collagen expression in cardiac fibroblasts, and inhibits H2O2-induced cardiomyocyte death and Ang II-induced cardiac hypertrophy. Furthermore, ERBB agonist-1 can prevent myocardial fibrosis and demonstrates cardioprotective effects in mouse models.