Atrial fibrillation, or AF for short, is one of the most common clinical arrhythmias. The incidence of atrial fibrillation increases with age, and atrial fibrillation has multiple hazards, the most serious of which is thrombosis and embolism of the body circulation. When a patient has an episode of atrial fibrillation, the left atrium loses its contractile function and is in a state of fibrillation, blood tends to stagnate in the atrium and form a thrombus. If the thrombus is dislodged, it can flow with the blood to all parts of the body, among which cerebral embolism is the most common and the most serious. Clinically, clinicians must recommend a transesophageal cardiac ultrasound prior to the conversion of atrial fibrillation or radiofrequency ablation, why is this? What is transesophageal cardiac ultrasound? How is it performed? Transesophageal echocardiography is an ultrasound probe placed in the middle of the esophagus to explore the deep structures from the back of the heart to the front, avoiding interference from the chest wall, lung gas and other factors, so it can show clear images, improve the sensitivity and reliability of the diagnosis of cardiovascular disease, and also facilitate the ultrasound monitoring and evaluation during cardiac surgery. Why must transesophageal cardiac ultrasound be performed? As mentioned above, thrombus is easily formed in the left atrial auricle of patients with atrial fibrillation, and transesophageal cardiac ultrasound is more disturbed and less likely to detect thrombus. Transesophageal cardiac ultrasound can avoid the influence of lung gas and chest wall, obesity and other factors, and because the probe is closer to the left atrium and atrial septum, it can detect conditions that cannot be easily detected by transthoracic cardiac ultrasound, such as left auricular thrombus, which can further avoid the complication of thrombus dislodgement. What are the risks of performing transesophageal cardiac ultrasound? Transesophageal echocardiography is a relatively mildly invasive test that is generally unresponsive, except for throat discomfort or mild nausea, and is tolerated by most patients. However, transesophageal cardiac ultrasound should not be performed in patients with extreme physical weakness, severe heart disease, persistent high fever, esophageal disease (such as esophageal varices, bleeding, esophageal strictures, diverticula or esophageal cancer), severe chest pain or severe coughing symptoms that cannot be relieved, or severe hypertension. In addition, possible complications during the examination include: severe nausea, vomiting, choking and coughing; allergic reaction to anesthetics; asphyxia due to accidental aspiration of oral contents into the trachea; severe cardiac arrhythmias (such as ventricular tachycardia, ventricular arrest, etc.); esophageal perforation, bleeding or local hematoma, etc. Therefore, it is important to understand the patient’s condition, master the indications and contraindications before the examination, and improve the upper gastrointestinal contrast in advance if necessary to avoid the occurrence of adverse events of esophageal perforation.