Systemic AL amyloidosis is a plasma cell disorder characterized by organ damage due to light-chain deposition, with cardiac involvement being a major determinant of prognosis. We report a case of a 50-year-old woman with suspected cardiac amyloidosis in whom less-invasive biopsies were inconclusive. Despite typical clinical, laboratory, and imaging findings, Congo red staining of fat and oral mucosa biopsies was negative. Definitive diagnosis was established by endomyocardial biopsy, which confirmed lambda light-chain amyloid deposits. The patient was treated with daratumumab-based therapy (D-VCd), achieving hematologic complete response with minimal residual disease negativity and cardiac improvement. This case highlights the key role of endomyocardial biopsy in establishingthe diagnosis of cardiac AL amyloidosis when non-invasive methods are inconclusive, enablingtimely and effective treatment.
