Congenital heart disease

Subaortic stenosis
It is very unlikely that SAS is present if no murmur is present at one year of age.   Most boxers (approx. 70%) with severe SAS will die suddenly by three years of age.

Pulmonic stenosis

Mitral valve disease
We have noticed a high incidence of (usually) mild mitral valve regurgitation in boxers that seem  otherwise to be normal.  In almost all cases this is quite mild and is not thougnt to ever become a problem for the individual.  The significance if this is unknown.

Heart muscle disease (Cardiomyopathy)
Heart muscle disease (cardiomyopathy) is well recognized in the boxer.  Several names are given in the literature to myocardial disease of boxers, such as boxer cardiomyopathy, boxer myocarditis, boxer dilated cardiomyopathy. Oftentimes it is not clear exactly what is being described.  The myocardial diseases seen in boxers probably vary in different regions of the country and it is not known if all of these is a single disease entity or not.

At least in the east, the term boxer cardiomyopathy refers to a problem that is by far the most common heart disease in the breed.  The cause is unknown and it is suspected to be genetically transmitted.  Boxers may be first affected at any age but are typically first diagnosed between the ages of six years and 10 years.  Prior to this, the disease may be undetectable.  The main problem boxers with this disease have is arrhythmias which may eventually be severe enough to cause syncope (fainting due to low blood pressure) or sudden death.  These boxers have an abnormal ekg with   progressively worsening arrhythmias as the disease runs its course over several years.  During this time, the echocardiogram is usually near normal.   Eventually, life threatening arrhythmias develope or myocardial failure occurs.  (Chronic tachyarrhythmias are known to induce myocardial failure.  It is not known whether this mechanism is present in boxer cardiomyopathy.)  Treatment for these arrhythmias does decrease the frequency of syncopal events.  It is not known whether or nor such treatment increases the individual's life expectancy.

The EKG. Many dogs, other breeds, have no VPC's or a very few VPC's on a 24-hour ekg.  The exact normal number of VPC's per 24-hour period of time for canine species, or the normal number of VPC's for the boxer breed is unknown.  At the present time 50 to 100 VPC's per 24-hour period is considered normal or near normal.  Whether or not a single 24-hour ekg is good enough to confidently indicate that boxer cardiomyopathy is likely to be present or not is unknown.  A 24-hour ekg is the most sensitive way to detect early cases.  This is critical for a breeding program.  For the affected individual, the benefits of treating an assymptomatic individual is unknown.