A heart murmur is a distortion of the heartbeat due to blood flowing back through a valve that should be closed.If the heart sound is lub-dub-ssshhh,the most likely cause is a failure of the
A)atrioventricular valves. B)semilunar valves. C)mitral (bicuspid)valve. D)AV node to signal contraction. E)sinoatrial node to signal contraction.