Murmurs are the result of turbulent or abnormal blood flow created by narrowed vessels, valves or abnormal openings between heart chambers. Although many puppies may have heart murmurs that are not the result of serious disorders, they can indicate life threatening developmental problems within the heart and its closely associated vessels. The dog's circulatory system is quite similar to that of humans. The heart has four chambers. The two upper chambers are the left and right atria, while the stronger, lower chambers are the right and left ventricles .
Blood exits the tissues , travels toward the heart, and enters the right atrium .
From there it moves into the right ventricle. Blood, now rich in oxygen, leaves the lungs through the pulmonary vein and enters the left atrium. The left atrium pumps blood to the left ventricle. The left ventricle is the most heavily muscled and, therefore, the strongest of the chambers. The left ventricle pumps blood through the great aorta, which supplies the body with blood and oxygen.