Twelve patients, showing advanced left bundle branch blocks with axial deviation toward the left (beyond -45 degrees) were studied by clinical, radiological and vectocardiographic examinations. All of them showed a marked cardiomegaly and half of them had also severe congestive heart failure. The left axial deviation may be connected to an asyncronism of the left ventricular activation, due to a delayed excitation of the antero-superior wall because of a lesion of the anterior fascicle. The authors think that this asynchronism of the activation should be evident in ECG test by a more delayed intrinsecoid deflection in aVL than in V6, as has been previously pointed out in the isolated anterior fascicular block. This ecgraphic datum was found in two patients only. The other possible causes of a left axial deviation in advanced left bundle branch block are discussed.