Transesophageal echocardiography (TEE) is an essential diagnostic tool in patients with poor transthoracic echocardiographic windows or when detailed imaging of structures distant from the chest wall is necessary. A real-time 3D TEE probe has been fabricated in our laboratory in order to increase the amount of information available during a transesophageal procedure. The 1 cm diameter esophageal probe utilizes a 2-dimensional, 5 MHz array at its tip with a 6.3 mm diameter aperture, including 504 active channels. The array has a periodic vernier geometry with an element pitch of 0.18 mm, built onto a multilayer flexible (MLF) interconnect circuit. In order to accommodate 504 channels within the device, a 1 m long Gore MicroFlat cable was utilized for wiring the MLF to the corresponding system connectors. Pulse-echo tests in a water tank have yielded a -6 dB bandwidth of 25.3%. Fully connected to the system through 3 m of cable, the probe shows an average 50 omega insertion loss of-85 dB with a standard deviation of 4 dB, as determined through pitch-catch measurements for a sampling of 10 elements. Using the completed 3D TEE probe with the Volumetrics Medical Imaging 3D scanner, real-time volumetric images of in vivo canine cardiac anatomy have been acquired, displaying atrial views, mitral valve function and interventional catheter guidance.