Just a very few years after Edler and Hertz had described the clinical use of M-mode echocardiographyl Satomura reported the application of Dop­ 2 pler ultrasound to the study of cardiac function. Yet Doppler ultrasound has been integrated into diagnostic practice in cardiology much more slowly than conventional (M-mode and two-dimensional) echocardiogra­ phy. Now, however, tremendous growth in the interest of clinicians in the diagnostic use of Doppler ultrasound can be observed and may in fact be due to the recent advent of color flow imaging. The reason for this growth may be that this method makes it possible to directly visualize the blood flow in the cardiovascular system in cross-sectional views. Moreover, the results are reproducible and much easier to understand than the older mapping techniques using a single-gate Doppler. In its short existence many different names have been used to describe this method, for instance, color Doppler, color flow imaging, real-time two-dimen­ sional Doppler echocardiography, and Doppler flow imaging. This diver­ sity reflects the large interest that many researchers have shown in this method. The technical development of color blood flow imaging (CBFI) - as this method will be called in this book - has not yet reached a universally accepted standard of performance in cardiology. Despite this state of flux and the uncertainty about future developments, I think it is justified to dedicate an entire book to this fascinating method.