OBJECTIVES: Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats and shares clinical and pathological characteristics with human HCM. Little is known about the pathogenic mechanisms underlying development of spontaneous feline HCM.

ANIMALS: The study population consisted of seven cats diagnosed with HCM and eight age-matched cats with no evidence of cardiac disease.

METHODS: Fresh myocardial biopsies taken from the middle of the left ventricular posterior free wall were obtained and examined with transmission electron microscopy.

RESULTS: Electron microscopic examination showed ultrastructural aberrations of the myocardial cytoarchitecture and of the interstitium in the seven cats with HCM. In the most severely affected cats the myofibrils were disorganized and subsarcolemmal mitochondria were depleted. In control cats, contraction band artifacts were commonly seen.

CONCLUSIONS: In this preliminary study we show that ultrastructural changes of the myocardium in seven cats with HCM involve the cytoskeleton and mitochondria. We suggest that our findings are important for future research aiming at elucidating the pathogenic mechanisms underlying the phenotypic expression of feline HCM. The results of this study prompt for a larger scale study, including quantitative measurements of mitochondrial distribution and cytoskeletal derangements in feline HCM.