This prospective study was conducted to determine the effect of Octreotide treatment on cardiovascular function in patients with active acromegaly. Ten acromegalic patients who failed to suppress growth hormone (GH) to < 5 mU/l during a 2 h oral glucose tolerance test were treated with 100 micrograms of Octreotide subcutaneously three times daily for 2 months, followed by 200 micrograms three times daily if the mean GH level was > 5 mU/l, for a total of 1 year. All patients had GH and insulin-like growth factor I (IGF-I) estimation, ejection fraction determined by Echocardiogram and multigated image acquisition scan, electrocardiogram (ECG), exercise ECG, 24-h ECG and chest x-ray. At 6 and 12 months, both GH and IGF-I were reduced but ECG, heart size and ejection fraction were unchanged. The patients improved symptomatically and had significant reduction in resting heart rate and increase in weight. Exercise time (mean +/- SD) increased from 637 +/- 137s at baseline to 787 +/- 101s at 1 year (p < 0.01) and work done increased from 9 +/- 3.3 to 11.9 +/- 2.7 metabolic equivalents (p < 0.001). We conclude that the decrease in GH and IGF-I following Octreotide treatment of acromegaly is accompanied by decreased heart rate and increased exercise capacity despite an unchanged ejection fraction.