<p>Zhilong Huoxue Tongyu capsule (ZL) is wildly used as a Chinese patent medicine for the treatment of cardiovascular diseases. Clinical studies have found that it can significantly improve hypertension and heart failure. However, its precise molecular mechanisms remain incompletely understood. The aim of this study was to investigate the effect of ZL on myocardial fibrosis (MF) in in vivo and its potential mechanisms. We established a hypertensive MF model by subcutaneous pumping of angiotensin II (Ang II) into mice, and validated in vivo whether ZL can reduce systolic blood pressure (SBP) and inhibit MF, including the use of echocardiography and various pathological staining techniques. Mechanistically, Western blot, qRT-PCR, and various immunostaining techniques were used to verify whether ZL can regulate TGF-β1/Smad3/Erbb4-IR/miR-29b pathway, and in vivo overexpression of Erbb4-IR was used to clarify whether it plays a key role in this pathway. ZL significantly reduced SBP in hypertensive MF mice, improved cardiac function and MF. Deposition of various collagen, expression of inflammatory factors, and activation of TGF-β1/Smad3 pathway is inhibited due to the intervention of ZL. In addition, ZL significantly reduced expression of Erbb4-IR and increased the expression of miR-29b. Mechanistically, after overexpression of Erbb4-IR in vivo, the regulatory effect of ZL on TGF-β1/Smad3/Erbb4-IR/miR-29b was reversed. Our results initially demonstrated ZL could exert cardioprotective effects in hypertensive MF mice. The pharmacological mechanism of ZL may be related to its regulation on TGF-β1/Smad3/Erbb4-IR/miR-29b pathway.</p>