1a. Valvular endocardiosis

1b. Endocardiosis is an idiopathic/degenerative change often found in older dogs. This must be distinguished from endocarditis which involves inflammation while endocardiosis does not.

1c. The mitral valve

1d.  Endocardiosis leads to valvular incompetence due to thickening of the valve .  With improper valve closure blood is regurgitated back into the left atrium during systole. The jet stream of blood going back to the atrium will cause increased turbulence and form a "jet" lesion (endocardial fibrosis) on the atrial wall. Rupture of the chordae tendinae may also occur.  Formation of thrombi on left atrium may occur with thromboembolism (i.e. to coronary arteries causing myocardial infarcts).  These inefficiencies can lead to congestive heart failure where the heart is unable to pump enough blood to meet the body's demand.  Rarely, rupture of atrial wall may occur (leading to cardiac tamponade).