A combination of an ultrasonic scanner and an omnidirectional receive transducer for producing a two-dimensional image from received echoes is described. Two-dimensional images with different noise components can be constructed from the echoes received by additional transducers. These can be combined to produce images with better signal to noise ratios and lateral resolution. Also disclosed is a method based on information content to compensate for the different delays for different paths through intervening tissue is described. The disclosed techniques have broad application in medical imaging but are ideally suited to multi-aperture cardiac imaging using two or more intercostal spaces. Since lateral resolution is determined primarily by the aperture defined by the end elements, it is not necessary to fill the entire aperture with equally spaced elements. Multiple slices using these methods can be combined to form three-dimensional images.