older, small breeds of dogs are prone to congestive heart failure due to degeneration of the mitral valve. this condition is known to be inherited in cavalier king charles spaniels. degenerative valve disease is the most common form of heart disease in dogs. mitral regurgitation leads to turbulent blood flow and increased pressure in the left atrium. this causes increased pressure in the pulmonary blood vessels and pulmonary edema (a build-up of fluid in the lungs). decreased output of blood by the left ventricle causes the body to compensate by increasing sympathetic tone and activating the renin–angiotensin–aldosterone system (raas). increased sympathetic tone leads to increased peripheral vascular resistance and increased heart rate and contractility of the heart muscle. chronic elevation of sympathetic tone damages the heart muscle. activation of the raas results in increased retention of water and sodium by the kidneys, blood vessel constriction, and other effects that result in increased blood volume. it also results in an increase in diastolic pressure and leads to pulmonary edema. treatment for congestive heart failure has historically focussed on two types of drugs that address these concerns: diuretics (especially furosemide), which decrease blood volume, and ace inhibitors, which interrupt the raas. recently, pimobendan - which increases the force with which the heart muscle contracts, and is also a vasodilator - is being more widely used in the treatment of congestive heart failure caused by valvular disease. a major veterinary study, called the quest study (quality of life and extension of survival time), published in september 2008 found that dogs with congestive heart failure receiving pimobendan plus furosemide had significantly better survival outcomes than those receiving benazepril (an ace inhibitor) plus furosemide. however, ace inhibitors and pimobendan have different mechanisms of action, and many veterinary cardiologists recommend they be used concurrently. within the past decade, a new surgical technique has been developed for mitral valve repair that replaces or strengthens the mitral valve chords with polytetrafluoroethylene (ptfe) prostheses and tightens the mitral valve ring to reduce or eliminate regurgitation.