Balloon mitral valvotomy (BMV) has become one of the most popular treatment modalities for mitral stenosis (MS). It has been traditionally performed with fluoroscopic and angiographic guidance, requiring right atriogram/aortogram for localization of the fossa ovalis, and bilateral cardiac catheterization for evaluation of the valvular functions. However, the indirect localization of the fossa ovalis may not be accurate and carries a potential risk of cardiac perforation. While hemodynamic evaluation of the severity of MS is the gold standard, that for mitral regurgitation (MR) is less reliable. Of course, left ventriculogram can quantify MR severity, but it would not be prudent to repeat ventriculography after each step of balloon dilatations, exposing patients to a large dose of radiation. To overcome these drawbacks, online transesophageal echocardiography (TEE) has been tried to guide BMV. It can directly visualize the fossa ovalis as well as the adjacent structures, thereby greatly decreases the risk of cardiac perforation. It can immediately evaluate MS and MR severities after each step of balloon dilatations, thus reducing radiation hazards and procedure time. In addition, using online TEE guidance, left heart catheterization could be omitted, further simplifying the procedure. In conclusion, online TEE is an appealing method for BMC, it can simplify the procedure and reduce radiation hazards and complications.