With current ultrasound technology, it is now possible to obtain accurate real-time and M-mode information from the fetal heart with the use of real-time--directed M-mode echocardiography. With this method, the M-mode cursor is directed to the fetal cardiac structures of interest while the image is obtained in the real-time mode. This enables M-mode echocardiograms to be obtained in an accurate, reproducible manner. The most useful imaging planes for cardiac evaluation are the long axis four-chamber plane, the short axis plane through the atrioventricular valves, and the short axis plane through the aortic and pulmonic outflow tracts. Once normal fetal cardiac anatomy is understood, structural defects and/or alterations of function can be evaluated accurately antenatally.