Endomyocardial biopsy of a 69-year-old female patient with a monoclonal gammopathy type IgG lambda. Interstitial amyloid deposits showed a homogeneous eosinophilic staining in the H&E-stained tissue section (A) and yellow-orange fluorescence in Congo red-stained sections (B). The amyloid deposits strongly immunoreacted with an antibody directed against TTR (C). No immunoreactions were found with antibodies directed against λ-light chain (D). A TTR mutation was detected (V30M), making the diagnosis of a hereditary ATTR amyloidosis. Original magnification ×200.