The heart operates with a pumplike action. Divided into four chambers-right atrium, right ventricle, left atrium, left ventricle-the heart has four valves that work to keep blood flowing in one direction. The valves open and close, letting blood in and then pumping it out. That sound is created from the movement of the valves and the flowing of the blood.

The sound a murmur makes depends on when it occurs in the cardiac cycle.

Correct auscultation of a puppy's heart at less than 8 weeks of age may reveal a heart murmur. This does not necessarily mean that there is a disease process occurring; however, it may.

To define a heart murmur, an often used example is the vibration felt, and the subsequent sound you hear, when you pinch a garden hose between your fingers with the tap fully turned on. What is heard when listening to the heart is a slurring of the normally distinct heart sounds. This may be a continuous slurring, or it may be intermittent at the point of each beat heard.

Heart murmurs are graded by intensity of sound, for instance on a scale of 1 to 6. It is not infrequent that one may hear a grade 1 or 2 heart murmurs in a 6-10 week old puppy. Often these murmurs disappear by the time the puppy is 12-18 weeks old, and are therefore termed innocent murmurs. However, murmurs with a greater intensity may mean that there is a congenital heart defect. Most grade 2 or lower will disappear by 18 weeks and the puppy will be fine with no long term or damaging effects. The puppy would be considered healthy and normal by 18 weeks. However, grade 3 usually or higher is a serious problem.

cardiac ultrasound exam is by far the most effective method of evaluating heart murmurs, I'd skip things like EKGs to get the ultrasound Exam, if a choice has to be made between tests.

A puppy at 8-12 weeks with grade 1 or 2 heart murmur would be considered innocent with the sale pending a clean bill of health by 18 weeks, free of murmur, (NOW GRADE 3 OR HIGHER WOULD NOT).

Because of the nature of many heart defects, their detection and classification is extremely important to any breeding program when a grade 3 or higher murmur is detected in more than 1 puppy or the whole litter has a murmur.

Thank You Helen for the help in this link!