Heart disease in felines usually comprises various forms of a defective heart muscle, or cardiomyopathy  (cardio = heart, myo = muscle, pathy = disease).
Felines most commonly develop one of  three different types:

DCM (Dialated Cardiomyopathy) leads to enlarged heart chambers due to a weakning of the heart muscle, and was relatively common until quite recently. Today it is rarely seen thanks to the adequate addition of Taurine in most main brands of cat food.

RCM (Restrictive Cardiomyopathy) is a form akin to HCM, and is often seen in older cats. It manifests itself in progressively poorer heart function with reduced  ability to pump.
This leads to an accumulation of blood in the heart, and an enlargement of the atrium.

By far the most common type of heart disease in felines is HCM (Hypertrophic Cardiomyopathy).
The rest of this article with deal mainly with HCM.
HCM, or Hypertrophic Cardiomyopathy, is a heart disorder in which the left wall of the heart grows and thickens. (Hypertrophic = thickening)

1. Normal feline heart
2. Feline hypertrophic cardiomyopathy

The enlargement of the muscle leads to a reduced ability of the ventricle to fill with blood.
This, in turn, leads to an accumulation of blood in the left atrium, and to an insufficient quantity of blood being pumped around the body.
The atrium expands and the blood accumulation at length becomes so large that the lungs are affected and start to fill with fluid (pulmonary edema) Heart failure occurs when the situation has progressed to the point where the heart can no longer compensate for the disorder.
An additional complication which might occur is the development of  blood clots (thrombi).
Due to  reduced circulation and the accumulation of blood in the atrium there is a danger that the blood may congeal and a blood clot may lodge at the branch of the aorta that supplies blood to the rear limbs, resulting in  partial or full paralysis (saddle thrombus).

Symptoms of HCM are most frequently seen in young and middle-aged male cats, usually before the age of 5-6, but have been recorded in cats as young as 8 months and as old as 16. Scientists are at present working to uncover the genetic predisposition to HCM, and there seems to  be a greater hereditary tendency among the Maine coon breed, where HCM is inherited as the dominant gene. Though it looks as if Maine coon and several other breeds are more susceptible to HCM, it must be stressed that any cat of any age is at risk.

Disclaimer: The information given on this page is meant solely as a general introduction to HCM and felines, and must not be taken as an alternative to a professional opinion. I am not a vet. If you suspect your cat might be ill, or it is acting unusually, you should contact a vet immediately. The information presented here has been gathered from various sources.
The symptoms of HCM vary greatly, from cats that are seemingly unaffected, to cats that die suddenly. Since cats are reclusive by nature, often the symptoms of cardiovascular disease are vague (as are those of other diseases in cats).
In those cases where the cat exhibits no visible or obvious signs of the disease, it may well be able to lead a normal life and the disease only becomes apparent and the symptoms suddenly appear when the cat experiences stress. Stress leads to a faster pulse, which means the heart has less time to expand and fill. As with all cardiac disorder, early detection and diagnosis is the key to the most successful clinical treatment.

The symptoms could be one or several of the following:
Lack of appetite
Increased weariness / lethargy
Less activity
Difficulty in breathing
Weight loss

With heart failure and fluid in the lungs, the symptoms might be fast and shallow breathing - often through open mouth, nasal mucous, coughing, severe lethargy, a weak and fast pulse and pale mucus membranes. The cat might become very weak, collapse, and in some cases, die.

Another serious symptom is paralysis of the lower back and rear limbs, or rear limb dysfunction.
The reason for this being a blood clot lodged in the lower part of the back. Paralysis could be a sign of a clinical emergency and is usually extremely painful. You should contact a vet immediately.

When it has got to the point where the cat is showing obvious clinical symptoms, the disease is usually well advanced.
Remember also, that symptoms vary from case to case. If you have the slightest doubt about your cats health, you should get in touch with a clinic. Its better to err on the side of caution.

Never give your cat aspirin or paracetamol without first having consulted a vet!
It may potentially poison the cat, as cats react very strongly to such medicines.

A suspicion of HCM and an enlarged heart in your cat  may arise before any symptoms become visible. If the cat is suffering from HCM, the vet might detect an irregularity of the heartbeat, or a heart murmur, in the course of the annual check-up. Such discovery prompts an ultrasound scan of the heart, which will reveal whether the heart is enlarged. With an ultrasound scan, an echocardiogram, the vet can determine just how enlarged the heart is, and assess its functioning.
As the heart grows, the heart valve function is affected, which the vet can detect using a physical principle called a colour doppler. ECG and x-ray are also helpful in determining HCM. Using x-ray it is possible to assess complications such as an enlarged heart and fluid in the chest cavity.
The vet can treat the cat for the symptoms and suffering which has been caused by HCM. If there is fluid in the lungs, the cat should receive a diuretic drug. At the same time, it is important to ensure that bloodclotting does not occur, and bloodthinning medications should be administered.

The vet will treat the actual heart disorder by giving the cat beta-blockers, which makes the heart beat slower. It also gives the blood more time to fill the heart chamber, and increase the pumping action.

If the disease can can be diagnosed at an early stage the cat can survive for a fairly long time.
Most cats showing no symptoms at the time the disease is diagnosed may live more than five years after the diagnosis. Cats arriving at the clinic with heart failure will survive for a much shorter period, on average 3 months, though one in five survive more than 3 years.
For cats who have thrown bloodclots, the prognosis is poor. They will not live, on average, for more than six months.
But even after experiencing bloodclots and pulmonary edema some cats, with the correct medication, may live at least another 2 years. 
Boris 1996 - 2002

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