A prominent Eustachian valve dividing the right atrium imaged by three-dimensional transesophageal echocardiography.

A 63-year-old man underwent transesophageal echocardiography (TEE) to rule out left atrial thrombi prior to cardioversion. Initial two-dimensional TEE with color flow Doppler imaging was suggestive of an atrial septal defect. However, three-dimensional TEE imaging revealed that the unusually large elongated Eustachian valve extended toward the superior vena cava and mimicked the interatrial septum, while the true septum was located more posteriorly than the Eustachian valve. Three-dimensional TEE imaging was crucial to understanding the anatomical relationship between the Eustachian valve and the interatrial septum and hence proved helpful in characterizing this unusual anatomical variant.