Aortic or pulmonic valve stenosis causes a systolic murmur when blood is discharged through the restricted orifice. When ventricular pressures drop during relaxation, regurgitation of the same valves causes a diastolic murmur as blood flows backward through the sick valve. The severity of these murmurs is an indication of how much damage there is to the valve. Pulmonary stenosis is usually found in infants and young children with left-to-right shunts such as patent ductus arteriosus or atrial septal defects. It occurs when blood pressure differences between the right and left sides of the heart cause the valve leaflets to calcify on the wrong side. This prevents them from closing completely, allowing more blood to flow toward the other side. As a result, there is increased stress on that side of the heart, leading to remodeling of the muscle fibers and eventual development of fibrosis. The only cure for this disease is surgery to replace the defective valve. Do not confuse pulmonary stenosis with asthma, which can also cause shortness of breath upon exercise. Do not confuse it with pneumonitis, which is an inflammation of the lungs that can be caused by many things including drugs, chemicals, or infections.