Cardiac amyloidosis is an infiltrative cardiomyopathy, resulting from amyloid deposition within the myocardium. In primary systemic (AL-type) amyloidosis, the amyloid protein is composed of light chains resulting from plasma-cell dyscrasia, and cardiac involvement occurs in up to 50% of the patients We present a case of a 43-year-old man, with complaints of periodical swollen tongue and xerostomia, bleeding gums and haematuria for two months. His blood results showed normocytic anaemia, thrombocytopenia and a high spontaneous INR, therefore he was referred to the Internal Medicine clinic. In the first visit, he showed signs and symptoms of overt congestive heart failure and was referred to the emergency department. The electrocardiogram showed sinus tachycardia and low voltage criteria. Echocardiography showed biventricular hypertrophy with preserved ejection fraction, restrictive physiology with elevated filling pressures, thickened interatrial septum and atrioventricular valves, small pericardial effusion and relative "apical sparing" on 2D longitudinal strain. Cardiac MRI showed diffuse subendocardial late enhancement. Serum protein electrophoresis was inconclusive, however urine analysis revealed nephrotic range proteinuria, positive Bence Jones protein and an immunofixation test with a monoclonal lambda protein band. Abdominal fat biopsy was negative for Congo red stain, nevertheless a bone marrow biopsy was performed, revealing lambda protein monoclonal plasmocytosis, confirming the diagnosis of primary systemic amyloidosis. This case represents a rare cause of heart failure in a young adult. Low-voltage QRS complexes and typical echocardiography features should raise the suspicion for cardiac amyloidosis. Prognosis is dictated by the level of cardiac involvement; therefore, early diagnosis and treatment are crucial.