Given the persistently high morbidity and mortality of heart failure (HF), targeting myocardial remodeling, particularly pathological hypertrophy and fibrosis, has become a major therapeutic priority. RhoA (Ras homolog gene family member A), a small GTPase governing cytoskeletal reorganization and cell migration, plays a pivotal role in this process. However, RhoA has long been considered undruggable because of its high-affinity binding to GDP/GTP and the absence of well-defined druggable pockets. Structural analyses comparing RhoA-GTP and RhoA-GDP conformations, combined with surface plasmon resonance-based screening, were used to identify a RhoA inhibitor. The underlying mechanism was validated in cultured cells and 3-dimensional myocardial tissue models. Therapeutic efficacy was assessed across multiple species of HF models and supported by multiomics analyses linking RhoA activation to human HF. Key findings were further confirmed by multiplex immunohistochemistry and pulldown assays in human heart specimens. We identified an unrecognized cryptic pocket adjacent to GDP in RhoA. A natural product, AH001, selectively occupied this pocket and interacted with GDP, thereby stabilizing the interaction between RhoA and its endogenous inhibitor, RhoGDIα (Rho GDP-dissociation inhibitor 1). AH001 suppressed downstream signaling by reducing MRTFA (myocardin-related transcription factor A) nuclear translocation and downregulating fibrosis- and hypertrophy-related proteins. Moreover, AH001 disrupted pathological crosstalk between These findings establish pharmacological inhibition of RhoA activation as a viable strategy to mitigate myocardial remodeling in HF and provide a conceptual framework for developing reversible inhibitors against previously undruggable small GTPases.