Systolic murmurs are graded on a scale of 1-6 while diastolic murmurs are graded on a scale of 1-4 (see below). Often, grade 1 murmurs are not discernable to inexperienced clinicians, while grade 6 murmurs are heard even without the stethoscope on the chest and may actually be visible. The intensity of a murmur is primarily determined by the volume/velocity of blood flowing through a defect and the distance between the stethoscope and the lesion. For example, a very thin patient with severe aortic stenosis with a high pressure gradient across the valve (thus high velocity of blood flow) will have a loud murmur. Conversely, the exact same valvular lesion in a morbidly obese person or a person with severe COPD and a widened anterior-posterior chest diameter may be inaudible.
Grading systolic murmurs
Audible, but soft
Easily audible and associated with a thrill
Easily audible, associated with a thrill, and still heard with the stethoscope only lightly on the chest
Easily audible, associated with a thrill, and still heard with the stethoscope off of the chest