An ECG gated ultrasonic imaging compounding system and method for synthesizing a cineloop of a compound ultrasonic image such as a cardiac cycle is presented. In real-time operation, a series of image frames may be recorded at a frame rate over a cardiac cycle and stored in a cineloop memory. A second series of image frames are recorded over a second cardiac cycle. The image frames of the second cardiac cycle are frame-by-frame aligned in time and space with the corresponding image frames from the cineloop memory. The aligned frames are then combined to form a series of synthesized image frames which then replace the original image frames in the cineloop memory. Subsequent series of image frames are also combined with the synthesized image frames in the cineloop memory to form new synthesized image frames which then replace the old synthesized image frames in the image array, and so forth. The series of image frames may be triggered to begin at a cardiac event such as the R-event.