This is a phase II clinical trial in which children with refractory infantile spasms (also called epileptic spasms or West syndrome) will be treated with fenfluramine, to evaluate efficacy, safety, and tolerability. Patients with infantile spasms that have not responded to treatment with vigabatrin and ACTH we will be invited to participate. Study participants will undergo baseline video-EEG, receive treatment with fenfluramine for 21 days, and then undergo repeat video-EEG to determine effectiveness. Patients with favorable response will have the opportunity to continue treatment for up to 6 months.