This may also be a secondary disease, occurring in conjunction with other cardiac abnormalities and may affect both the left and/or right ventricles.
Clinical signs are usually severe in onset and commonly seen at a young age (often 4 - 6 months of age) and develop rapidly.
Generalized weakness, exercise intolerance, syncope, ascites, hepatomegaly and pale mucus membranes are present. A cough may be present intermittently. Tachypnea, tachycardia and a bounding pulse are frequently observed in advanced cases.
A definitive diagnosis requires postmortem examination of the heart.
Gross and histological examination of the heart often reveals a diffuse fibroplasia over the ventricular endocardial surface with microscopic bands of mature fibrous connective tissue in the myocardium of the left ventricle. The fibroplasia frequently extends into the adjacent myocardium associated with cardiomyocytic and Purkinje fibre degeneration.
A differential diagnosis would include ventricular septal defect, double-chambered right ventricle, hyperthyroidism, cardiomyopathy, endocardial amyloidosis, endocarditis, mitral valve endocardiosis, other causes of congestive heart failure and infections with Dirofilaria spp.
A possible association with canine parvovirus infection has been postulated by not proven, and seems unlikely due to the absence of any microscopic inflammatory disease associated with this condition.
Surgical correction can be performed at specialty referral centers via balloon valvuloplasty.
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