In the puppy, the most frequently diagnosed abnormalities are those associated with the circulatory system. All puppies should have their initial veterinary exam by twelve weeks of age so the heart functions can be monitored. Most congenital
heart defects can be detected at this early age with the aid of a stethoscope. Many heart defects cause abnormal heart sounds called murmurs. 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. The right ventricle pumps blood from the body into the lungs to exchange carbon dioxide (produced by cellular metabolism) for oxygen. 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.
The chambers are separated from one another by muscle and a series of valves. The atrioventricular valve separates the right atrium and right ventricle, while the mitral valve separates the left atrium from the left ventricle. Each chamber and valve must function in a coordinated effort in order for the heart to pump efficiently.
Congenital heart and vessel defects
Blood from the fetus travels through the umbilical cord where it receives oxygen from the mother and waste products and carbon dioxide are passed to the mother. The lungs serve no function until birth, at which time the infant is exposed to breathable air. Blood in the fetus therefore bypasses the lungs and flows directly from the right heart chambers to the left via a vessel called the ductus arteriosus. At birth, the ductus arteriosus closes off forever, forcing blood to flow through the lungs for the oxygen/carbon dioxide exchange. Similarly within the fetus, vessels bypass the liver until birth. The fetus depends on the mother's liver to provide needed functions. At birth, the vessels close and the infant's blood is then routed through the puppy's liver.