Abstract: The purpose of this study was to find out the primary spectral features in the cardiac shunt diseases, by analyzing and comparing the pulsed Doppler flow spectrum of various cardiac positions in 60 normal subjects and 40 patients with cardiac shunt diseases. Among the four features such as the timming, spectral form, flow direction and frequency shift amplitude, the timming is the most important one for the clinical diagnosis. In 40 patients detected by ultrasonic pulsed Doppler technique, 38 patients were confirmed by surgery, with 1 patient being false negative, and another one, false positive.