Normal QRS axis ?

Ans. is 'b' i.e., -30 to +110deg In a normal hea, the average direction of the vector during spread of the depolarization wave through the ventricles, called the mean QRS vector, is about +59 degrees. This means that during most of the depolarization wave, the apex of the hea remains positive with respect to the base of the hea. The normal electrical axis of the hea (mean electrical axis or mean QRS vector) lies between -30deg and + 100deg. If the axis is more negative than -30deg it is called left axis detion, whereas if the axis is more positive than + 100deg, it is called right axis detion.