Natural closure can occur in the fetal period, and 76% of those that do not close before birth close within the first year of life; it usually occurs more often within 3 years of age and less often in older children or adults. Ventricular defects in the membranes and trabeculae are more likely to close spontaneously, while ventricular defects in the outflow tract, near the pulmonary valve and poorly aligned ventricular defects rarely close spontaneously. Small ventricular defects have a high chance of spontaneous closure, but perimembranous ventricular defects larger than 10 mm or those with previous cardiac insufficiency also have a chance of spontaneous closure. The probability of spontaneous closure of large ventricular defects (defects that cause pulmonary artery pressure to exceed 50% of the pressure in the body circulation) is usually likely to be low.