A 60-year-old man with coronary artery disease, ischemic cardiomyopathy with biventricular implantable cardioverter–defibrillator placement, and atrial fibrillation presented with chest pain and numbness in both arms. During his initial presentation, he suddenly collapsed and became unresponsive. Computed tomographic (CT) angiography of his chest, abdomen, and pelvis was performed to evaluate the possibility of aortic dissection. The images showed gas in the left ventricle (Panel A). Further review revealed gas in the left atrium with a connection to the esophagus (Panel B). His family later reported that he had undergone radiofrequency ablation for atrial fibrillation 6 weeks earlier. The gas in the heart was thought to be from an atrial–esophageal fistula that may have developed after this procedure. Imaging also showed renal infarcts, probably from air emboli. Findings from brain imaging were unremarkable, but the patient remained without notable neurologic function. His family elected against surgery, given his poor prognosis. The patient died a few hours after his initial presentation. An atrial–esophageal fistula can be a complication of radiofrequency ablation and is associated with a substantial risk of death. Chest CT is the preferred diagnostic test for this condition; transesophageal echocardiography should be avoided because intubating the esophagus can cause further gas embolization.