Atrial dilation or fibrillation on dogs and cats allows abnormal eddying and stasis of blood within the atria. Thrombosis may occur with subsequent embolisation of thrombus and lodging in smaller vessels. This particularly occurs in the cat where thrombi lodge in the femoral artery. The platelets within the thrombus release vasoactive amines which potentiate the hypoxia by constricting collateral circulation to the hindlimb. The cat will present with an acute hind limb paralysis with the limbs affected being cold to the touch and without a femoral pulse.
Embolism elsewhere is usually clinically silent.