Dilated cardiomyopathy associated with acromegaly is rare, but may improve with octreotide, a somatostatin analogue. The authors give the first description here of paradoxical worsening in cardiac function during such treatment, with the onset of episodes of acute decompensation following each attempt at starting treatment. Thus worsening was confirmed objectively by a challenge test with octreotide: increased dyspnea, fall in shortening fraction and in echocardiographic cardiac output (of 17 to 14% and 4 to 3 l/min respectively), a decrease in isotopic ejection fraction from 15 to 6% and this in parallel with efficacy regarding hormone levels of GH and IGF1 and a reduction in tumour size by CT scan. No further episode of decompensation occurred after treatment was stopped permanently. The patient underwent a transplant 3 months later. Suppression of the positive inotropic effect of GH by octreotide, associated with an increase in peripheral resistance is suggested. A negative inotropic effect of this hormonal analogue on too advanced a case of heart disease is also a possibility.