Pulmonary arterial hypertension (PAH) is a fatal disease marked by increased pulmonary vascular resistance and right ventricular (RV) failure. Impaired vascular relaxation and vasoconstrictive signaling, including Rho-associated kinase (ROCK2) upregulation and myosin phosphatase target subunit 1 (MYPT1) downregulation, contribute to disease progression. We investigated the therapeutic effects of URO-K10, a novel K7.4 channel activator, in a monocrotaline-induced rat model of PAH (PAH-MCT). In PAH-MCT rats, chronic URO-K10 administration improved body weight gain, and significantly reduced RV hypertrophy. Functional studies revealed enhanced pulmonary artery relaxation, while relaxation after high K+-induced contraction showed only partial recovery. Immunoblot analysis demonstrated that ROCK2 upregulation was reversed by URO-K10, but MYPT1 remained downregulated and MLC2 diphosphorylation persisted. Interestingly, treatment with 8-Br-cGMP restored delayed relaxation and reduced MLC2 phosphorylation in URO-K10-treated PAH-MCT while not in the untreated PAH-MCT rats, suggesting that cGMP supplementation can compensate for the recovery from impaired endogenous signaling by the URO-K10 application. These findings suggest that URO-K10 improves pulmonary hemodynamics and RV remodeling via K7.4 activation and downregulation of ROCK2. However, incomplete recovery of MYPT1 and MLC2 phosphorylation highlights the complexity of contractile regulation in PAH. K7.4 activation represents a promising therapeutic approach but may require combination strategies to fully restore vascular function in PAH.