A 50-year-old male presented with signs and symptoms of restrictive heart disease. A right ventricular endo-myocardial biospy revealed deposition of extracellular eosinophilic hyaline material. On transmission electron microscopy, this material is most likely to reveal the presence of-
Restrictive cardiomyopathy along with deposition of extracellular eosinophilic hyaline material suggest the diagnosis of Amyloidosis
Myocardial involvement with amyloid is a common cause of secondary restrictive cardiomyopathy. Amyloid is a pathological proteinaceous substance deposited between cells in various tissues and organs of the body.
With the light microscopic and standard tissue stains amyloid appears as an amorphous, eosinophilic, hyaline extracellular substance, that with progressive accumulation encroaches on and produces pressure atrophy of adjacent cells.

Physical nature of amyloid :
Electron microscopy
On electron microscopy, amyloid is seen to be made up largely of non branching fibrils of indefinite length and a diameter of approximately 7.5 to 10 nm
X-ray crystallography and infrared spectrum
This demonstrates a characteristic cross β pleated sheet conformation
Non branching filaments of indefinitive length
Cross banded fibres with 67 m periodicity
Weber Palade bodies
Concentric whorls of lamellar structures