Chronic valvular disease is an idiopathic degenerative process of the valves of the heart leading to valvular insufficiency.  Chronic mitral valve insufficiency (CMVI) is the most common cardiovascular disorder in dogs, being exceedingly common in older patients of small breeds.  CMVI is a progressive disorder that changes with time, necessitating periodic reevaluations.  The mitral valve (MV) is the separation between the left atrium (LA) [ which receives blood from the lungs ] and the left ventricle (LV) [ which distrubutes blood to the body ].  Consequently, degenerative processes of the MV can lead to anatomic and functional abnormalities of LV and circulatory system, LA and lungs, and secondary, the right side of the heart and its function.  Normally the mitral valve functions to allow flow from the LA to the LV and to prevent flow from the LV to the LA.  As the mitral valve degenerates with age, it begins to leak and some fraction of blood flows back into the LA instead of forward to the body.

The decreased forward flow may cause the pet to feel weak, unable to exercise or loss of appetite.  Other problems such as kidney disease may result as well.  The increased backward flow into the LA causes extra blood to remain in the heart.  With time the heart must stretch or dilate to accommodate this extra volume.  A dilated heart is more prone to arrhythmia (irregular heartbeat).  When stretching is at its limit, blood backs up into the lung vessels causing pulmonary edema (fluid), then the right side of the heart, then the abdomen causing the liver to enlarge and eventually fluid to accumulate in the belly.  The enlargement of the LA and LV can also induce arrhythmia of the heart that may need to be addressed.  The most common sign of progressing CMVI is coughing.  Animals may also show an increased respiratory (breathing) rate (greater than 60 breaths per minute at rest) and an increased effort of breathing.  Occasionally animals may also collapse or faint.  These signs, as well as any significant change in your pets attitude, activity or appetite should be closely monitored and reported.

In general, the goal of therapy is to improve the length and quality of life with medication.  Surgical repair of the mitral valve is still considered experimental.  To date, there is no indication that any therapy administered in the absence of clinical signs will delay the onset of symptoms or prolong survival.  Therefore, a realistic goal of therapy remains the palliation of clinical signs (coughing, fainting…).  Exercise restriction and low salt diets can be aids in the treatment of your pet.  Primarily, multiple drugs can be used depending on your dog’s individual hemodynamic and cardiac needs.  Many, if not all of the medications used for your pet will need to be continued throughout his/her life.  Because of the progressive / dynamic nature of CMVI, and because no medications are without at least some side-effects, routine reevaluation of your pet is needed in order to provide optimal care.