Pulmonary arterial hypertension (PAH) is a rare, progressive, and incurable disease characterized by an elevated pulmonary blood pressure, extensive remodeling of the pulmonary vasculature, increased pulmonary vascular resistance, and culminating in right ventricular failure. Mitochondrial dysfunction has a major role in the pathogenesis of PAH and secondary right ventricular failure, and its targeting may offer therapeutic benefit. In this study, we provide proof-of-concept for the use of the mitochondrially active drug SUL-150 to treat PAH. PAH was induced in rats by monocrotaline, followed by the placement of an aortocaval shunt one week later. The mitoprotective compound SUL-150 (~6 mg·kg·day) or vehicle was administered intraperitoneally via osmotic minipump for 28 days, implanted at the time of aortocaval shunt placement. Vehicle-treated PAH rats had dyspnea and showed pulmonary artery remodeling with increased responsiveness to phenylephrine, in addition to remodeling of the intrapulmonary arterioles. SUL-150 administration mitigated the dyspnea and the remodeling responses. Vehicle-treated PAH rats developed right ventricular hypertrophy, fibrosis, and failure. SUL-150 administration precluded cardiomyocyte hypertrophy and inhibited ventricular fibrogenesis. Right ventricular failure in vehicle-treated PAH rats induced mitochondrial loss and dysfunction associated with a decrease in mitophagy. SUL-150 was unable to prevent the mitochondrial loss but improved mitochondrial health in the right ventricle, which culminated in the preservation of right ventricular function. We conclude that SUL-150 improves PAH-associated morbidity by the amelioration of pulmonary vascular remodeling and right ventricular failure and may be considered a promising therapeutic candidate to slow disease progression in pulmonary arterial hypertension and secondary right ventricular failure.