A man and his father each developed atrial fibrillation after the ingestion of a frozen sweet. In the son, atrial fibrillation recurred with the subsequent ingestion of cold beverages. Neither patient had documented episodes of atrial fibrillation at any other time. The son also had multiple other episodes of palpitation, suggesting brief episodes of atrial fibrillation, and these occurred only with the ingestion of cold substances. Possible mechanisms include direct cooling of the left atrium through the wall of the esophagus and autonomic stimulation by the cold substance.