Pulmonary stenosis is a congenital heart defect in which the pulmonary valve doesn't open properly. The pulmonary valve is between the right ventricle and the pulmonary artery. It opens to allow blood to flow from the right ventricle through the pulmonary artery to the lungs. This forces the right ventricle to pump harder than normal to overcome the obstruction. In most children, the obstruction can be relieved by a procedure called balloon valvuloplasty. Others may need open-heart surgery.