Device closure of secundum atrial septal defect (ASD) has emerged as an appealing alternative to surgical repair. It has traditionally been guided by online echocardiography. Currently, there are two methods for online echocardiographic guidance, namely, transesophageal echocardiography (TEE) and intracardiac echocardiography (ICE). For online TEE guidance, the TEE probe is inserted just prior to balloon sizing. The heart is scanned from 0 to 180 degrees to rule out any unsuspected findings such as thrombus. Then, the bicaval view is used during balloon sizing to measure the balloon-stretched or flow-limiting diameter of the ASD, and to assure that no residual shunt is present. Just before its deployment, the position of the device is checked. It should be located in the main atrial cavity, not in the atrial appendage. Device deployment is monitored with online TEE. Finally, following the "Minnesota wiggle" and before detachment of the device, a multiplane scanning is repeated to make sure that no part of the device herniated, and the adjacent structures (such as right pulmonary vein, vena cavae, coronary sinus and atrioventricular valves) are not compromised. Online TEE guidance for ASD closure can be performed either with general anesthesia (with or without endotracheal intubation), or without. While the former is suitable for pediatric patients, the latter, in experienced hands, could be performed for most adults. It is proven to be versatile, convenient and cost-effective.