(+)-Norfenfluramine a major hepatic metabolite of (+)-fenfluramine, is a selective 5-HT 2B receptor agonist ( K i : 11.2 nM). (+)-Norfenfluramine potently stimulates the hydrolysis of inositol phosphates and increases intracellular Ca 2+ . (+)-Norfenfluramine can be used for the research of primary pulmonary hypertension and valvular heart disease.