Heart disease is relatively common in cats. Some heart defects, eg hole in the heart, are present from birth (congenital heart defects) but may only cause signs as the animal gets older. Other diseases develop later in life as a result of the effects of ageing or damage to the heart.
The signs of heart disease are often very similar whatever the cause. Many of the signs of heart disease can be confused with natural ageing changes. Reduced energy and increased sleeping are common. Cats with severe heart disease often have poor appetites and may lose weight. If water retention occurs as a result of the heart failure you might not notice that your cat is losing weight. Other signs of heart failure are difficulty in breathing due to fluid build up in the lungs - but remember these signs may be seen with many other diseases too. Less commonly, cats with heart disease may faint or collapse.
In almost all cases the sooner heart disease is recognised and treated the better the outcome will be. If you are worried about your cat in any way always seek further advice from your vet.