Critical pulmonary stenosis causes cyanosis and can be potentially lethal in the neonate. Initial treatment includes general resuscitation and infusion of prostaglandin E1 to dilate the ductus. The diagnosis is usually made echocardiographically, but a right ventriculogram in the outflow tract may be necessary in some patients with only a tiny valve opening. Preformed catheters may aid in the passage of an appropriate guidewire. Valvuloplasty should be performed with a balloon approximately 1.2 times the annulus diameter. Most patients remain mildly to moderately cyanotic immediately after the procedure. With right ventricular (RV) growth and improved RV compliance, the cyanosis eventually resolves. Some patients may require prolonged prostaglandin infusion, a surgical shunt, or other mechanical means of maintaining systemic-to-pulmonary artery flow. Intermediate--to long-term results are excellent. However, only 5%-10% of patients may require surgical relief of residual valve or subvalvular stenosis. Very long-term follow-up raises concern about the significance of induced pulmonary insufficiency. Up to 30% of patients may require repeat balloon valvuloplasty.