The purpose of this study is to evaluate changes in left ventricular mass and cardiac function in patients with active acromegaly before and after treatment with the growth hormone receptor antagonist pegvisomant for one year.

Inclusion Criteria:

• Active acromegaly in adult subjects (≥ 18 years) after surgery and/or radiation therapy with elevated IGF-1 levels despite treatment with somatostatin analogues or dopamine agonists
• Pegvisomant therapy is indicated (i. e. patients who have had an inadequate response to surgery and/or radiation therapy and/or other medical therapy, or for whom these therapies are not appropriate)
• Evidence of left ventricular hypertrophy (infero-lateral wall thickness ≥ 12 mm assessed by echocardiography) or
• Evidence of impaired diastolic function (≥ stage 2 as assessed by echocardiography) or
• Evidence of systolic dysfunction (Ejection fraction < 50% assessed by echocardiography)
• Stable medication for arterial hypertension and heart failure for 3 months
• Written informed consent.

Exclusion Criteria:

• Pregnancy and lactation period
• Previous therapy with Pegvisomant
• Suspected or known hypersensitivity to the drug or any of its components
• Contraindications for MRI
• History of malignancy during the last 5 years
• Suspected or known drug or alcohol abuse
• Patients who are neither able to self administer study medication on a daily basis nor have a caregiver who can administer study medication to the patient on a daily basis
• Any condition which in the opinion of the investigator makes the patient unsuitable for inclusion
• Participation in another clinical trial
• Pituitary adenoma with a distance to the optic chiasm of < 3 mm
• Any other drug for treatment of acromegaly (e.g. dopamine agonists, Somatostatin analogues) which would be necessary during the study or patients who apply for radiotherapy
• Instable heart insufficiency classified as NYHA IV.
• Severe renal insufficiency, liver transplantation