If QRS deflection is large and positive in lead II and 0 in aVL. What is his mean electrical axis in the frontal plane?

When the vector in the hea is in a direction almost perpendicular to the axis of the lead, the voltage recorded in the ECG of this lead is very low. Conversely, when the hea vector has almost exactly the same axis as the lead axis, essentially the entire voltage of the vector will be recorded. aVL=0, means mean cardiac axis is almost perpendicular to aVL, i.e., either 60 or -120 degrees. Depolarization moving toward an active electrode in a volume conductor produces a positive deflection, whereas depolarization moving in the opposite direction produces a negative deflection Large positive wave in lead II means depolarisation wave is travelling towards lead II i.e. mean cardiac axis must be +60 degrees.