Three neonatal cases of muscular ventricular septal defect (VSD) without other cardiac anomalies were presented, which were detected using color Doppler echocardiography. Spontaneous closure confirmed by the disappearance of both the murmur and shunt flows was observed in two of the three cases whose ages were 1.5 and 4.5 months, respectively. Furthermore, in the third case, it probably closed by 4.5 months of age, because the shunt flow was difficult to detect by color Doppler. Color Doppler seems to be useful for detecting small shunts of muscular VSD and for observing their spontaneous closure. Though the incidence of muscular VSD in Japan is rare and most of them may be spontaneously closed early in infancy, its detection is expected to increase in the future and the confirmation of their natural closure may become easy by the wide use of color Doppler echocardiography.