A 3D ultrasonic diagnostic imaging system produces 3D cardiac images at a 3D frame rate of display which is equal to the acquisition rate of a 3D image dataset. The volumetric cardiac region being imaged is sparsely sub-sampled by separated scanning beams. Spatial locations between the beams are filled in with interpolated values or interleaved with acquired data values from other 3D scanning intervals depending upon the existence of motion in the image field. A plurality of different beam scanning patterns are used different ones of which have different spatial locations where beams are located and beams are omitted. A sequence of different beam scanline patterns may be continuously repeated or the patterns of the sequence synchronized with the cardiac phases such that over a sequence of N heartbeats the same respective phase is scanned by N different scanline patterns. Fig.1
