Though some cases involve severe symptoms shortly after birth, this defect is usually diagnosed during the investigation of children with heart murmurs and no other symptoms and is rarely recognized in adulthood. The degree of obstruction may remain stable or increase, depending on how the pulmonary valve changes in response to the patient's growth. In adulthood, there may be an increase in obstruction as calcification of the valve sets in and arrhythmias may develop.

Besides the evaluation of the patient's heart murmur, diagnosis and severity are based on electrocardiography (ECG), chest x-ray, MRI (Magnetic Resonance Imaging), and/or echocardiography. The ECG provides non-quantitative information on severity of the stenosis and will appear normal if the obstruction is mild. Enlargement of the pulmonary artery is often seen with the chest x-ray, though the degree of enlargement does not correspond to the degree of stenosis. The overall anatomy of the heart and the defect itself may be seen on the MRI and echocardiogram. The echocardiogram also permits a good estimate of the degree of obstruction. A cardiac catheterization procedure may be performed to accurately determine the degree of obstruction, measured by the difference in blood pressure between the right ventricle and pulmonary artery and for intervention (pulmonary balloon valvuloplasty).

Medical management is important to monitor the degree of obstruction and to guard against the development of congestive heart failure. In more severe cases, the patient will experience fatigue, breathlessness (dyspnea), and (rarely) chest pain in response to exertion. Mild cyanosis may also be observed (right to left shunting across a Patent Foramen Ovale). However, most people with pulmonary stenosis have no external symptoms.

Significant stenosis usually causes hypertrophy (thickening) of the wall of the right ventricle. This may lead to a further narrowing of the right ventricular outflow tract, which can cause failure of the right ventricle and a decreased tolerance for exertion. In some cases, especially for those over 40, there is the risk of sudden death in the absence of treatment.

Surgical or balloon valvuloplasty is recommended for moderate to severe stenosis. This operation involves very low risk and an excellent prognosis for a long and active life after surgery. Children and young adults may be treated by balloon valvuloplasty during a cardiac catheterization procedure, which opens the pulmonary valve, decreasing the stenosis. The replacement of the pulmonary valve may be necessary in older patients whose valves have become substantially calcified and/or insufficient.

Medical follow-up is usually considered to be unnecessary for mild cases of pulmonary stenosis.