Acromegaly is associated with an increased cardiac morbidity and mortality, but it is not clear whether this is the result of increased incidence of hypertension and coronary heart disease or of a specific disease of heart muscle. Thirty four acromegalic patients were studied by non-invasive techniques. Seven of these patients had raised plasma concentrations of growth hormone at the time of study; three were newly diagnosed and had not received any treatment. Hypertension was present in nine (26%) but only three (9%) had electrocardiographic left ventricular hypertrophy. Echocardiography showed ventricular hypertrophy in 12 (48%) and increased left ventricular mass in 17 (68%) patients. Holter monitoring detected important ventricular arrhythmias in 14 patients. Thallium-201 scanning showed evidence for coronary heart disease in eight patients. Systolic time intervals were normal except when there was coexistent ischaemic heart disease. A comparison between 19 acromegalic patients with no other detectable cause of heart disease and 22 age matched controls showed appreciably abnormal left ventricular diastolic function in the group with acromegaly. The abnormalities shown did not correlate with left ventricular mass or wall thickness. There was no difference in diastolic function between patients with active acromegaly and those with treated acromegaly. Hypertensive acromegalic patients had worse diastolic function than hypertensive controls, suggesting that hypertension may further impair the left ventricular diastolic abnormality in acromegaly. This is the first study to find evidence of subclinical cardiac diastolic dysfunction in acromegaly and it supports the suggestion that there is a specific disease of heart muscle in acromegaly.