Heart Murmur in Dogs Grade Levels

Heart murmur in dogs can range from minor to severe and can impact the quality of life for the dog. Depending on the grade and type of heart murmur, some dogs can live with little or no impact, while other dogs may be somewhat limited in their lives because of their heart condition. The key to understanding heart murmurs in dogs is to understand the anatomy and function of the heart, as well as what the heart murmur grades in dogs indicate.

Overview of the Heart

In dogs, the heart is divided into 4 chambers, the right and the left. The uppermost chambers are known as the left and right atria, while the lowermost chambers are known as the left and right ventricles. There are four valves, each with flaps, within the heart. These four valves include:

• Tricuspid valve – right atrium/right ventricle
• Pulmonic valve – right ventricle/pulmonary artery
• Mitral valve – left atrium/left ventricle
• Aortic valve – left ventricle/aorta

The sole purpose of these valves is to open and close in order to keep blood flowing in one direction. Upon stethoscope examination, a veterinarian will hear the normal beat of the heart, and no extra sounds will be heard. However, when a dog has a heart murmur, a veterinarian will actually hear a swooshing sound in between the normal beating of the heart, which indicates that the valves are opening and closing but creating a backward flow of blood. This means that one of the heart valves is not functioning properly.  

Heart Murmur Grade Levels

Heart murmurs in dogs are clinically labeled with 6 different levels, and each level is used to indicate the severity of the murmur, the amount of medical intervention needed, and the overall effect on the dog. These levels actually indicate how loud the heart murmur is, and therefore how serious the condition is.

• Grades 1 and 2 are considered very quite and possibly inaudible. Sometimes only the most qualified of veterinarian cardiologists can hear a heart murmur at these levels. This level of heart murmur in dogs typically does not require medical intervention.
• Grades 3 and 4 are described as moderately loud to loud. During these stages, dogs typically present with clinical signs of a heart murmur, including shortness of breath and persistent cough. This may be the beginning stage of congestive heart failure in dogs.
• Grades 5 and 6 are the loudest of all murmurs are may not require a stethoscope to be heard. The term “thrills” is also associated with these types of murmurs as the sound of the heart murmur may actually be felt on the dog’s chest wall with manual palpation. At this point, medication will be imminent for the dog, and surgery to repair the weakened valves may also be an option.

Detecting Heart Murmurs

The first step of diagnosing heart murmurs in dogs is listening with a stethoscope. If an abnormal sound is heard, typically at the 3rd or 4th level, the next step would be to have an electrocardiogram or an echocardiogram done to measure the overall function of the heart and further diagnose the condition of the dog.