Hypertrophic Cardiomyopathy (HCM)
This information is not meant to be a substitute for veterinary care.
Always follow the instructions provided by your veterinarian.
Anatomy of the heart of a cat
HCM is a disease that causes thickening of the heart muscle
resulting in poor relaxing and filling ability. As the heart’s pumping
chamber (ventricle) becomes progressively thicker, less blood can enter the
chamber; thus, less blood is ejected out to the body. The cause of HCM is
unknown, although certain breeds of cats appear to be predisposed.
Middle-aged male cats may be more commonly affected. Sometimes heart muscle
thickening similar to HCM can develop secondary to other disorders such as
hyperthyroidism (elevated thyroid hormone) and systemic hypertension
(elevated blood pressure). Blood pressure measurement and, in cats over five
years of age, a blood thyroid hormone test should be done to exclude these
secondary causes when cardiac hypertrophy (thickening) is diagnosed.
Some pets show no sign of illness, especially early in the disease. In
other cases, signs of left-sided congestive heart failure (fluid
accumulation in the lung) may occur. These signs include lethargy,
decreased activity level, rapid and/or labored breathing
and possibly open mouth breathing with excitement or exercise. Sometimes
left and right-sided congestive heart failure develop with fluid
accumulation inside the chest or abdominal cavity causing greater
respiratory (breathing) effort and abdominal distention. Once fluid
accumulations have occurred, clinical heart failure is present and
aggressive medical therapy should be sought. Other signs of this disease can
include sudden weakness, collapsing episodes, and unfortunately even
sudden death due to disturbances in heart rhythm. In some cats with a
very large heart chamber (i.e. left atrium) a blood clot may form and if it
enters the circulation may cause weakness or paralysis (usually of the
rear legs). If this occurs, contact your veterinarian right away to
determine if complications related to heart disease (or another disease) are
A physical examination performed by your veterinarian may reveal a heart
murmur, abnormal heart sounds, abnormal lung sounds, or irregularities in
heart rhythm. Chest radiographs (x-rays), an electrocardiogram
(ECG..sometimes called an EKG), and an echocardiogram (heart ultrasound) are
tests often utilized to confirm a suspected diagnosis and to determine
severity. A routine physical exam and one or more of these tests may be
recommended every six months to one year to look for any progression of
disease in cats without clinical signs.
Asymptomatic pets may not need medical therapy depending on the findings
of the tests listed above, but routine reevaluations will often be
recommended. Other cats will need medications to slow the heart rate, and
promote relaxation of the pumping chambers (ventricles). If arrhythmias or
congestive heart failure signs are present, additional medications used may
be required. Since this disease can be progressive, the number and the
amount of medications used may change with time. Therapy is always tailored
to the needs of the individual patient. If congestive heart failure is
present, dietary salt reduction is also recommended.
Medications commonly used for HCM:
Beta-adrenergic blockers such as atenolol (Tenormin) or propanolol
(Inderal). These medications slow the heart rate, which enhances filling and
relaxation of the pumping chambers. Beta-blockers also allow more time for
blood flow to the heart muscle itself, and reduce the amount of oxygen used
by the heart. In some cases, the incidence of arrhythmias is also lessened.
Side effects may include bronchospasm (spasm of the airways) (propranolol),
fatigue, and in excessive doses, slow heart rate and low blood pressure.
Calcium-channel blockers such as diltiazem (Cardizem CD, Dilacor
XR). This class of drug has similar actions to the beta-blockers. Some
differing characteristics of the calcium-blockers include little or no
anti-arrhythmic activity in some cases, possible a greater ventricular
relaxing effect, and a greater propensity for low blood pressure at higher
Other medications may be prescribed in some patients. Diuretics (furosemide,
spironolactone, etc.) may be needed to control edema and effusions
(congestive heart failure). In pets that have had or may be prone to blood
clot formation, anti-coagulants such as aspirin, warfarin, or heparin may be
Medical therapy is always chosen to meet the needs of the individual
Frequent recheck examinations and adjustments may be needed especially
early in the course of treatment to individualize a medication regimen.
This Pet Health Topic was written by
O. L. Nelson, DVM, MS,
Diplomate ACVIM (Cardiology & Internal Medicine) Washington State
Washington State University assumes no liability for injury to you or
your pet incurred by following these descriptions or procedures.
top of page
||Did you find this information useful? Please
consider helping us train the veterinarians of tomorrow by making a
gift to the college.
The Pet Health Topics Web site is a free
service provided by the College of Veterinary Medicine at Washington
State University. Your donation will help support veterinary
education and research.