Generalized weakness can be a warning sign of heart disease. Your pet may be unable to walk or stand, walk unsteadily, or walk with a limp. In pets with heart disease, weakness is caused by a diseased heart pumping less blood to the body and the muscles.
Cats with heart disease can develop a sudden onset lameness or paralysis, essentially a sudden inability to move a limb. The most common cause of rear limb paralysis in cats is a blood clot that goes to the back leg, called a saddle thrombus or arterial thromboembolism (ATE). This clot blocks blood flow to the affected limb(s). A clot in the back leg suddenly causes the cat to be unable to put full weight on the affected leg. The cat may be vocalizing, usually a sign that the leg is painful. The leg might feel cool to the touch. The clot usually affects both rear legs, but can affect only one rear leg, a front leg, or other parts of the body.
This video shows a cat 3 days after experiencing an arterial thromboembolism (ATE). He is able to move around, but still dragging one hind limb. Often when an ATE first occurs the affected limbs do not move at all.
The development of a clot is an emergency. Veterinary care should be sought immediately.