In the puppy, some of the most frequently diagnosed abnormalities are those associated with the circulatory system. All puppies should have their initial veterinary exam by eight to 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.
Puppies may develop a physiologic or innocent murmur which will disappear usually by four to five months of age. Physiologic murmurs are the result of rapid growth and do not cause disease. If a murmur is pathologic, it can indicate life threatening developmental problems within the heart and its closely associated vessels.
A Lesson on Canine Heart Anatomy
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 of the body, travels toward the heart via the blood vessels, 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 four chambers. The left ventricle pumps blood through the great aorta, which supplies the body with oxygen rich blood.
The heart chambers are separated from one another by muscle and a series of valves. The tricuspid 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 pup takes her first breath. Blood in the canine fetus therefore bypasses the lungs and flows directly from the main pulmonary artery to the descending aorta 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. In some puppies, the ductus arteriosus remains open, resulting in a condition called patent ductus arteriosus (PDA).
Septal defects are holes in the walls of the heart that did not develop normally. Septal defects can occur in the walls of the atria or the ventricles. These defects allow blood to flow from one side of the heart to the other, bypassing the lungs or the rest of the body.
Be sure to have your puppy examined by your veterinarian as soon as possible. Diagnosing a congenital heart defect and seeking treatment early can improve your puppy's prognosis and quality of life.
Article by: Race Foster, DVM and Angela Walter, DVM