HCM…a silent killer

This condition (cardio..heart; myopathy…muscle disease) is characterized by idiopathic left ventricular posterior wall and interventricular septal concentric hypertrophy. In short…the walls of the left side pumping chamber of the heart become very thickened and the lumen of this chamber becomes very tiny. This causes ventricular dysfunction primarily during the filling phase (diastole) of the heart beat.

Cardiomyopathies can cause congestive heart failure, cardiac arrythmias, sudden death and systemic arterial embolism (saddle thrombus).

Effective management of cardiomyopathy requires an accurate diagnosis.

This condition is a silent killer because many cats show no outward signs of HCM before it is very advanced or until their heart rate is elevated due to stress, pain, drugs etc.. Clues that HCM may be present include, but are not limited to, nonspecific signs of illness such as poor appetite, depression, inactivity or reluctance to move. Difficult and/or rapid breathing may be noticed, however a cough is very unusual. Some cats present with hind limb paralysis and severe pain due to thromboemboli.

In most cases clues to this condition are detected during routine physical examinations. The sad thing is many owners decline the further investigation that is required to definitively determine the presence of HCM. Auscultation of the chest (listening to the heart with a stethoscope) often reveals a heart murmur. A murmur is an abnormal heart sound caused by turbulent blood flow. The loudness or tone of a murmur is not directly proportional to the seriousness of the underlying abnormality. Often very quiet murmurs are caused by very serious heart problems.Arrythmias, abnormal heartbeat sequences, such as gallop rhythms, may be detected. In cats with HCM the heart rate is often faster than normal. In many cases the murmur and/or gallop rhythm is only detected when the cat is stressed and the heart rate is fast. Thus, when the stethoscope is first applied to the chest wall and the cat is anxious these changes may be detected only to disappear as the cat relaxes and the heart rate lowers. This does not mean that the cat is normal after all. On the contrary..it can be the first clue to detecting a lethal heart condition and should not be underestimated!

Cases that present as emergencies often exhibit open mouth breathing and sternal recumbency. The mucous membranes may be blue due to poor oxygenation. As mentioned previously some present with painful hindlimb paralysis.

If your cat has a murmur of any loudness or a gallop rhythm..even if transient..it warrants further investigation. Chest radiographs showing the cardiac silhouette and an ECG can be indicative of HCM.  However cardiac ultrasonography (echocardiography) is the diagnostic tool of choice in confirming and categorizing HCM.

Other conditions can result in thickening of the left ventricular wall. Hyperthyroidism and systemic hypertension should be ruled out as possible underlying causes. In cats with concurrent diabetes Acromegaly should be considered. In young cats, or those with long standing cardiac murmurs, the underlying cause could be congenital aortic stenosis or mitral valve dysplasia.

In order to effectively treat heart disease it is imperative that it is properly diagnosed and any underlying conditions be determined and addressed.

Cats suspected of having HCM should:

Have a thorough physical examination
Have appropriate blood and urine tests run
Have chest and abdominal radiographs taken and/or
Have an ultrasound (echocardiography) performed …if possible by a veterinarian Board Certified in this field.


The treatment required will depend upon the type and severity of the diagnosed heart condition plus the nature of any underlying or concomitant problems. Treatment/management of heart disease depends on the type and severity of the diagnosed heart problem. Ongoing research and clinical studies are constantly bringing new information to this field of veterinary medicine.


Early detection and treatment/control lends to a more favorable prognosis. Even in more advanced cases with a history of pulmonary edema or a resolved thromboembolism, some cats, on appropriate medication, may live comfortably for quite some time.

If you love your cat…
Please do not ignore or belittle the significance of heart murmurs and/or arrythmias. They truly can be silent killers.