The clinical signs of dogs affected with MVD include signs of left sided congestive heart failure such as exercise intolerance, cough, dyspnea and syncope. Cough is usually associated with an elevation of the left main stem bronchus secondary to left atrial enlargement resulting from mitral valve regurgitation. The cough is generally described as a hacking dry cough which often occurs after exercise and excitement or at night. Some brachychalic breed dogs such as Pug may have concurrent tracheal stenosis, bronchitis, or other respiratory problems which can cause coughing. Therefore, the diagnosis of MVD should be performed carefully to rule out the exact underlying cause of the cough. Syncope may be related to insufficient forward flow, pulmonary hypertension and/or cardiac arrhythmias (Pedersen and Häggström, 2000). A major finding in physical examination of MVD dogs is a systolic murmur loudest at the apex of the heart on the left thorax secondary to mitral valve regurgitation. Precordial thrill can also be palpable in dogs with severe mitral valve regurgitation. The intensity of murmurs can be used to subjectively evaluate the severity of degeneration secondary to its strong correlation with the severity of valvular thickening and the size of left cardiac chambers assessed by echocardiography
(Häggström et al., 1995).