While the use of ultrasonic techniques for medical applications is well established, obtaining quantitative information from such techniques remains difficult. The development of the range-gated, pulsed Doppler provides depth information but without reference to any coordinate system. A new position locating system is under development utilizing the transit times of sound waves. This system will allow for determining the location in 3 dimensional space of the ultrasound beam axis and hence the location of the range-gated sample volume. Accuracies on the order of 1 mm are expected. It will then be possible, through the use of a microcomputer, to locate various anatomical sites on the heart thereby yielding information on various cardiac dimensions. 0 The system can also be applied to determining the orientation of the sound beam axis with respect to the flow axis of major vessels. Such a capability will allow for the solution of the Doppler equation yielding quantitative information on velocities. The system under development provides superior resolution to instrumented, articulated arms. A major advantage of this technique is that the transducer will not be mechanically constrained and the physician will be free to operate over the chest surface. BIBLIOGRAPHIC REFERENCES: "Analysis of an Ultrasonic Spatial Locating System," William E. Moritz, Peter Shreve and Les Mace, IEEE Trans. Instrumentation and Measurements, March, 1976. "A Microprocessor Based Spatial Locating System," William E. Moritz and Peter Shreve, IEEE Proceedings, June, 1976.