High cardiac output as a paraneoplastic syndrome. A high cardiac output (17 1 min-1) was recorded in a young man suffering from lymphoplasmatocytotic lymphoma. The evolution of the blood disease was characterized by two relapses, during which clinical signs of heart failure were prominent but resolved with efficient blood chemotherapy. The known aetiologies of high cardiac output were excluded. The complete normalization of the cardiac parameters with blood remission suggests that the high cardiac output represented an unusual paraneoplastic syndrome, the pathogenesis of which still remains unknown, although several hypotheses were tested. 