Ventricular tachycardia with left bundle branch block appearance in adults without coronary artery disease may be due to arrhythmogenic right ventricular dysplasia. This condition forms part of a spectrum with the complete form of Uhl's anomaly at one end and arrhythmogenic right ventricular dysplasia at the other. Both conditions have similar histological appearances representing the same congenital defect but the macroscopic appearances are quite different. Arrhythmogenic right ventricular dysplasia seems to be a slowly progressive condition with one or more localisations in the right ventricle where the myocardium is replaced by adipose tissue with progression of lesions from the epicardium towards the endocardium. The subepicardial layers resemble a plexiform structure of partially degenerated myocardial fibres within fibro-adipose tissue. These fibres may be the site of slowing of activation and the anatomical basis of intraventricular reentry phenomena. A similar appearance is also found in UHl's anomaly, but the severe dilatation of the ventricle and almost complete absence of muscle fibres only leaves a few zones with surviving, partially degenerated myocardial fibres. Clinically, a cardiothoracic index of over 0.60 is more common in Uhl's anomaly whilst arrhythmogenic right ventricular dysplasia is usually associated with a normal cardiac silhouette or only slight cardiomegaly. The differential diagnosis is important if surgery is being considered. An appropriate technique must be chosen to avoid supraventricular arrhythmias which can lethal in patients with Uhl's anomaly.