Standard computed tomographic scanners have limited applicability in cardiac studies due to a relatively long image acquisition time of 1 to 3 seconds. Since the heart contracts at frequencies that usually exceed one cycle/second, cardiac images obtained with standard tomographic instruments do not allow for discrimination of cardiac geometry at specific points of the cardiac cycle. Clinically useful images of the cardiac chambers can be obtained by employing prospective or retrospective gating of conventional computed tomographic images or utilizing specially designed computed tomographic instruments that obtain images in a fraction of a second. The first rapid computed tomographic scanner, the Dynamic Spatial Reconstructor, designed by Earl Wood and Eric Ritman at the Mayo Clinic, is able to obtain computed tomographic images in 10 msec. A more practical device for obtaining rapid computed tomographic images at 50 msec intervals has been developed by Boyd at the University of California, San Francisco. This device is commercially produced by the Imatron corporation (Imatron C-100). It employs an electron gun to generate an X-ray beam which can be guided around the patient with a magnetic field. In this brief review, we will describe two general cardiac applications of ultrafast computed tomography — studies of left and right ventricular function and size, and studies of vein bypass patency and flow reserve. All the data reported had been obtained with the Imatron C-100 scanner.