Udenafil is an inhibitor of phosphodiesterase 5 (PDE5). In vivo, udenafil (1 and 5 mg/kg) increases lung cGMP levels, attenuates the development of compensatory right ventricular hypertrophy, and reduces pulmonary arterial wall thickening in a rat model of monocrotaline-induced pulmonary hypertension. It increases...