Aripiprazole is a novel antipsychotic with a pharmacodynamics profile that distinguishes it from other antipsychotics. Aripiprazole is a partial agonist at dopamine D2 receptors, a partial agonist at serotonin 5-HT1A receptors, and an antagonist at 5-HT2A receptors. Studies have shown that the atypical antipsychotic aripiprazole is effective and well tolerated in the treatment of acute bipolar manic and mixed episodes. Aripiprazole is recognized as one of the antipsychotics associated to the least cardiovascular effects in addition to having a low incidence of long QT, but there isn’t any aripiprazole induced premature ventricular contractions reported. We describe a patient who developed premature ventricular contractions after treatment of aripiprazole. A 40 year old male patient was hospitalized because of mixed episode of bipolar disorder. The patient was taking 900 mg/day of lithium. Aripiprazole (10 mg/day) was added on treatment. On the second day of aripiprazole add-on treatment, he had developed palpitation, shortness of breath, sweating. He hadn’t any cardiovascular disease before the admission. Twelve lead electrocardiogram and 24- hour Holter monitoring showed premature ventricular contractions. Aripiprazole was switched to risperidone 2 mg/day. Neither palpitation nor shortness of breath was experienced after the switch. Premature ventricular contractions induced aripiprazole treatment is an unexpected side effect. The mechanism of the premature ventricular contractions in this case is unknown, but might be caused by a change in ion channels, because some drug-induced arrhythmias account for acquired long QT syndrome. Premature ventricular contractions have been implicated in the development of left ventricular dysfunction and cardiomyopathy. If the clinician decides to begin aripiprazole treatment, cardiac effects must be kept in mind.