A necessary percursor to real-time three-dimensional echocardiographic imaging is the ability to obtain multiple planes of acoustic data simultaneously. A new ultrasound imaging technique facilitates the display of two real-time orthogonal B-mode images (O-mode). The O-mode technique uses a novel two-dimensional transducer and system processor to interrogate the two perpendicular planes simultaneously, yielding sector arcs that share one origin. It permits simultaneous display of two sector arcs on a single monitor either side by side or in a two-dimensional projection designed to convey the three-dimensional nature of the acoustic data. Clinical results from the first 50 patients undergoing O-mode evaluation indicate that image quality in the two simultaneously obtained planes is equal to that of a single plane when the system is operating in its conventional format. These data confirm the feasibility of real-time multiplane imaging. The system design offers the potential for the future addition of more simultaneous planes and, thus, the possibility of real-time three-dimensional ultrasound imaging.