Cardiac procedures rely on fluoroscopy for catheter guidance and visualization. However, fluoroscopy provides poor contrast of myocardial structures and exposes both the patient and health care providers to ionizing radiation. As an alternative to fluoroscopy, real-time three-dimensional (3-D) ultrasound imaging has the potential to provide a safe means for tracking catheter position in 3-D while simultaneously imaging the heart's anatomy. A method is described for locating a catheter-mounted transducer in the 3-D ultrasound imaging field. The distance from the imaging transducer to the catheter transducer is measured by time of flight, while the angular position is determined by a spatial crosscorrelation of the received signals with stored receive profiles. Results from simulations with 20-dB SNR demonstrated a mean accuracy of 0.22/spl plusmn/0.13 mm at a 70-mm range. In vitro testing showed a resolution of 0.23/spl plusmn/0.11 mm at a range of 75 mm and a resolution of 0.47/spl plusmn/0.47 mm at a range of 97 mm. With combined catheter position and imaging, this tracking method has the potential to replace fluoroscopy and enhance interventional procedures.