Isolated muscular ventricular septal defect was identified in 9 of 159 consecutive preterm neonates by color Doppler echocardiography, a prevalence of 56.6/1,000 live births. The neonates with ventricular septal defects appear clinically healthy, and in 87.5% of them the defect spontaneously closed within 6 to 11 months. The prevalence and rate of spontaneous closure are similar to those in full-term neonates.