Despite advances in the treatment of patients with pulmonary arterial hypertension (PAH), survival has not improved greatly (is still very affected). Imatinib, an antagonist of platelet-derived growth factor with antiproliferative activity, has been effective in experimental models and clinically in several published reports. We report the results of imatinib therapy in 4 patients with PAH (functional class IV) who were refractory to treatment with drug combinations for this condition. The final outcome was favorable in only 1 of the 4 cases. In this case, the patient was in functional class III and his hemodynamic parameters had improved significantly within 5 months after starting therapy. However, the patient died as a result of severe toxic hepatitis in which imatinib may have played a role. The present report adds to the few already in the literature (4 cases) and suggests that care should continue to be shown when using imatinib to treat PAH.