Absence of all of these pathologic findings provides confidence that the pulmonic flow murmur is not associated with an atrial left to right shunt or pulmonic valve stenosis. This murmur begins after the first heart sound and is best heard underneath the right clavicle. The murmur generally is grade II but can be grade III and usually is of short duration, occupying less than one half of systole. Murmur frequency is low and is diamond shaped with a somewhat noisy quality. The murmur radiates towards the neck particularly on the right.
Respiration has no effect.
The murmur intensity decreases significantly when the child sits with the shoulders hyperextended by bringing the arms behind the patient. This murmur is caused by turbulence in the major brachiocephalic arteries as these vessels arise from the aorta. The only innocent continuous murmur is a venous hum. This murmur begins shortly after the first heart sound and is located just beneath the right sternoclavicular junction with the patient sitting. It lasts throughout all of systole and approximately two thirds of diastole.