Cause
As an animal ages, its heart valves become thickened, distorted, and stiff due to the accumulation of polysaccharides, or complex carbohydrates. The abnormal functioning of the valves results in the regurgitation of blood back through the closed valve, increased pressure within the atria of the heart, decreased blood pumped out of the heart, activation of compensatory mechanisms, and congestive heart failure. The resulting volume overload within the heart leads to dilation of the ventricles and impaired ventricular function. All of these problems worsen and lead to even further dysfunction of the heart. It is also possible for the atria to tear, resulting in acute symptoms such as weakness and acute collapse.