The timing of a murmur in relation to the components of the cardiac cycle is the most useful characteristic in defining the cause of a murmur. A murmur may be classified as systolic, diastoic or continuous. The systolic murmur may begin simultaneously with the first heart sound prior to the opening of either the aortic or pulmonary valve. Such a murmur results from either a ventricular septal defect or atrioventricular valve regurgitation. It can help determine that a murmur begins with S1 by listening in an area where heart sounds are loud in relation to the murmur and then listening listening where the murmur is loudest. Click on listening area A = S1 audible, and note how clearly S1 is heard. Then listen to Area B = murmur obscures S1, and note that the increased intensity of the murmur obscures S1, despite the fact that S1 intensity has not changed.