Normal QRS axis -

Ans. is 'b' i.e., -30 to +110dego In a normal heart, the average direction of the vector during spread of the depolarization wave through the ventricles, called the mean QRS vector, is about +59 degrees,o This means that during most of the depolarization wave, the apex of the heart remains positive with respect to the base of the heart.o The normal electrical axis of the heart (mean electrical axis or mean QRS vector) lies between -30* and +10o If the axis is more negative than -30(r) it is called left axis deviation, whereas if the axis is more positive than + 100deg, it is called right axis deviation.