OBJECTIVE Our study was designed to demonstrate that transesophageal echocardiography using a 3.3-mm monoplane probe can accurately evaluate the left atrium for patients with arrhythmias before cardioversion. BACKGROUND Standard probes cause discomfort during intubation requiring sedation, but miniature probes do not. METHODS With topical anesthesia alone, a 3.3-mm probe was used for transesophageal echocardiography in 60 patients. After intravenous sedation, standard transesophageal echocardiography was then performed. RESULTS In 51 of 60 patients, the left atrium was visualized with the 3.3-mm probe. In 43 of 51 patients the appendage was clear. A thrombus was seen in 7 patients on both studies. In one patient spontaneous echocontrast was seen only with the 3.3-mm probe (sensitivity 100%, specificity 97%). In 9 of 60 patients, the appendage could not be assessed. CONCLUSIONS In many patients the 3.3-mm probe can visualize the appendage and obviate the need for sedation. Technical advances will improve image quality with miniature probes.