High cardiac output failure/state (HCOF) is regular feature of some illnesses e.g. thiamine deficiency, hyperthyroidism, severe anemia, Paget's disease or arteriovenous fistulae. HCOF in multiple myeloma is reported quite rarely. 31-year-old man was admitted because of fatigue, dyspnea and subfebrilities. Heart rate was 116/min, sinus rythm blood pressure 110/60 mmHg. Chest film showed cardiomegaly with sings of interstitial pulmonary edema, echocardiography mild dilatation of the left ventricle with hyperkinetic wall motion and small pericardial effusion. Hemoglobin was 104 g/l, leukocyte count 13.5 x 10(9)/l with 30% of plasmatic cells. Serum protein electrophoresis demonstrated a monoclonal gammapathy, X ray studies of the skelet multiple osteolytic lesions. Diagnosis of plasmocytic leukemia-form of multiple myeloma was established and chemotherapy (vincristine + adriamycine + dexamethason) was started. Patient cardiac status deteriorated. Cardiac catheterisation demonstrated mean righ atrial pressure of 25 mmHg, mean pulmonary artery pressure of 28 mmHg and pulmonary artery wedge pressure of 24 mmHg. Co was 20.0 l/min (C.I. 11.5 l/min/m2). In continuing of chemotherapy and symptomatic therapy for heart failure patients status gradually improved and complete remission of the myeloma and normalisation of cardiac parameters was achieved. Heart failure in multiple myeloma patients has been attributed to amyloidosis of myocardium, hyperviscosity syndrome, co-existing CAD or anthracycline toxicity. HCOF should be considered in patients with clinical evidence of heart failure and normal left ventricular function.