[The left-fascicular blocks ("hemiblocks")].

The left ventricular impulse conduction system is composed of two, three or more fasciculi. The blocking of the impulse in one fasciculus is termed a left fascicular block or "hemiblock" for short. The anatomical variations of the left ventricular impulse conduction system, and the possibility of partial blocking, makes the electrocardiographic diagnosis more difficult. The ECG criteria of left fascicular blocking - with special regard to the left anterior fascicular block - and their combinations with the right block (bilateral bifascicular block) are discussed. A bilateral trifascicular block without total AV block (in presence of a third left ventricular fascicle) is diagnosable in the ECG. The limits of electrocardiographic diagnosis of the fascicular impulse conduction disorders are shown and the importance of anamnestic and clinical data are emphasised with regard to therapy. Frequency and etiology of fascicular blocking are noted.