Methylene blue (MB), a potent inhibitor of nitric oxide (NO) synthase and soluble guanylyl cyclase (sGC), can treat vasoplegia but may antagonize pulmonary arterial hypertension (PAH) drugs that enhance the NO-sGC-cyclic guanosine monophosphate (cGMP) pathway. The gene discussed is SGCB; the disease is pulmonary arterial hypertension.