A morbidly obese patient is reported who underwent insertion of a BioEnterics Intragastric Balloon (BIB) as a pre-surgical procedure (ie. prior to restrictive gastric banding). While carrying the BIB, the patient suffered an episode of severe supraventricular tachyarrhythmia (atrial fibrillation). Although such an event is not definitely correlated to the BIB, the episode led us to modify the pre-treatment protocol, introducing dynamic Holter ECG into the work-up investigations and excluding subjects with a pathological cardiac rhythm.