The aim of the study was to investigate the effects of 1-yr treatment with octreotide (OCT) on left ventricular diastolic and systolic func- tion, assessed at rest and during physical exercise by gated blood pool cardiac scintigraphy, in 30 patients with active acromegaly. OCT was initially given at a dose of 0.05- 0.1 mg, 3 times daily, and the dose was subsequently increased to achieve GH/insulin-like growth factor I (IGF-I) normalization. Hormone normalization after treatment was considered when basal and/or oral glucose test-sup- pressed GH values were below 2.5 and 1 mg/L, respectively, and IGF-I values were within the normal range for age. To evaluate the response to OCT treatment in terms of cardiac performance, the 30 patients were divided into 2 groups on the basis of normalized (in 13 patients) or nonnormalized (in 17 patients) circulating GH and IGF-I levels. At study entry, hypertension was found in 6 patients (20%), ab- normal left ventricular diastolic filling was found in 12 patients (40%), and impaired left ventricular ejection fraction was found in 2 patients at rest (6.6%) and in 18 patients at peak exercise (60%). Before OCT treatment, exercise duration ranged from 6 -10 min, and exercise workload ranged from 50 -125 watts. After 1-yr treatment with OCT, a significant decrease in circulat- ing GH and IGF-I levels was achieved in all patients, but normal- ization was obtained only in 13 of 30 patients. In patients achieving circulating GH and IGF-I normalization after OCT treatment but not in those with persistently elevated hormone levels, a significant de- crease in heart rate, both at rest (from 75.7 6 3.3 to 66.5 6 2.9 beats/min; P , 0.01) and after exercise (from 137.5 6 4.9 to 123.7 6 4.1 beats/min; P , 0.01), and a significant increase in left ventricular ejection fraction, both at rest (from 56.5 6 1.8% to 66.5 6 2.2%; P , 0.01) and after exercise (from 52.6 6 2.4% to 67.1 6 1.7%; P , 0.01), were found. In the 17 patients who had persistently high circulating GH and IGF-I levels after 1 yr of OCT treatment, left ventricular ejection fraction was unchanged at rest but was significantly reduced after exercise compared to the basal value (from 64.9 6 2.4% to 57.2 6 2.6%, P , 0.01); systolic blood pressure at rest was significantly increased (from 128.5 6 4.9 to 141.2 6 5.4 mm Hg; P , 0.05). In these 17 patients, the ejection fraction response to exercise was signifi- cantly impaired, mostly in those less than 40 yr of age (from 11.6 6 3.2% to 20.3 6 5.6%; P , 0.05). In particular, among 9 patients who had a normal response to exercise at study entry, 6 developed an abnormal response after 1 yr. Left ventricular diastolic filling was unchanged by OCT treatment in all patients. Exercise duration (only in young patients from 7.5 6 0.5 to 9.3 6 0.7 min; P , 0.05) and exercise workload (in all 13 patients from 80.8 6 6.4 to 92.3 6 5.9 watts; P , 0.05) were significantly increased in the group of patients with normalized GH and IGF levels, but not in the remaining 17 (from 7.6 6 0.4 to 7.5 6 0.4 min and from 89.9 6 5.5 to 84.4 6 4.5 watts, respectively). In conclusion, the results of the present study indicate that sup- pression of basal or glucose-suppressed GH levels below 2.5 or 1 mg/L, respectively, together with normalization of plasma IGF-I levels for 1 yr are followed by a significant improvement, but not complete normalization, of left ventricular ejection fraction either at rest or at peak exercise without significant changes in diastolic filling. By con- trast, the persistence for 1 yr of elevated hormone levels caused a significant increase in systolic blood pressure and impaired cardiac performance. These data suggest that prolonged suppression of cir- culating GH and IGF-I levels could normalize cardiac performance and probably reverse the poor prognosis for cardiovascular disease in acromegaly. (J Clin Endocrinol Metab 84: 17-23, 1999)