In a prospective study on 340 cases with primary myocardial disease, eight patients (six males, two females, mean age 36 years, range 24-47) with an idiopathic left ventricular aneurysm were observed. All patients had normal coronary arteries, no angina or history of myocardial infarction; all but one had no risk factors for ischaemic heart disease; all had normal right ventricles; one patient had a history of familial dilated cardiomyopathy, two of 'flu-like' syndrome at the time of first symptom and two of alcohol abuse. All patients had ventricular tachycardia (VT), five sustained (of right bundle branch block morphology in three, and of different morphologies in two), three non-sustained. Patients with sustained VT had inducible VT (resembling the clinical one) on electrophysiological study. Electrocardiogram (ECG) showed an infarction pattern in three cases. Aneurysms were of limited size (2.1 +/- 1/11 segments on echocardiography) and were located in the septum, apex or posterior wall. Left ventricular ejection fraction (LVEF) was reduced (< 0.50) in six patients and was not correlated with the aneurysm size. The duration of illness was inversely correlated with LVEF (P < 0.05). Endomyocardial biopsy showed evidence of diffuse pathological changes in all cases (cell hypertrophy, myofibrillar lysis, mitochondriosis). During follow-up (64 +/- 32 months), patients were successfully treated with anti-arrhythmic drugs: no patients required surgical treatment to control ventricular arrhythmia. Considering the clinical and pathological features of idiopathic left ventricular aneurysm, this primary myocardial disease could be classified as a novel peculiar form of cardiomyopathy.