A heart murmur is the vibration of the heart caused by abnormal blood flow in the heart. The heart is divided into right and left sides and has four chambers-two atria and two ventricles- and the valves between each part of the heart control the flow of blood within the heart and to the lungs and the rest of the body. Each chamber of the heart has a one-way valve to keep blood from flowing backward. The valve between the left atrium and left ventricle is called the mitral valve and the valve between the right atrium and right ventricle is called the pulmonary valve. Heart murmurs are classified by the volume and strength of the vibration on a scale of one to six. A grade one heat murmur is barely audible through a stethoscope while a heart murmur of six are very loud and can be heard without the aid of a stethoscope if you simply place your ear near the dog’s chest on the left side you can feel and hear the strong vibration with your hands and ears. There are many, many causes of heart murmurs. Some are due to congenital defects: malformations of the heart and its blood vessels. Anemia or a low red blood cell count can cause a murmur as can a fever and puppies sometimes have unexplained low-grade murmurs that disappear as they mature. Inflammation or permanent scarring of the valves of the heart is a common cause of heart murmurs especially in older dogs. Many dogs develop heart murmurs as the result of dental disease because bacteria from the teeth get into the blood system that then ends up infecting the valves. Cardiomyopathy, abnormal thickening or thinning of the muscular walls of the heart can cause a murmur. Heartworm disease can also cause a heart murmur not only because the worms obstruct the flow of blood but also because the heart becomes enlarged as it tries to continue pumping blood around them. Once your veterinarian has diagnosed a heart murmur x-rays are taken to help determine what is the underlying cause. Cardiac ultrasound is often used to measure all the anatomic parts of the heart, as well as the speed of the blood flow through each of them. Veterinary cardiology is well-advanced and the causes of most heart murmurs can be successfully treated, although your pet may require medication and close monitoring for the rest of their life.