This report describes the design considerations, performance characteristics and initial clinical results of a new, high-resolution, real-time, two-dimensional ultrasound sector scanner designed specifically for cardiac use. Such a system is unique as it relies upon phase-array principles, rather than mechanical means, to steer the sound beam through the target volume. The prototype system uses a linear array of 16 ultrasound transducers which are resonant at approximately 2 MHz. At the site of contact, the array currently in use measures 24 by 14 mm, where the latter dimension corresponds to the elevation dimension of each of the 16 active elements.