Given a standard 3-lead ekg where the leads are read as below: Why does atrial depolarization cause an upward deflection? Assuming the EKG is being read from Lead II, I believe that if the current flowing from the negative terminal at RA (right arm) to the positive terminal at LL (left leg) is positive, then atrial depolarization (whose current moves parallel to this vector from upper right heart to lower left heart) would cause a positive summation of currents leading to the upward deflection. However, why would Lead II (which runs from negative terminal to positive) cause a positive current? Doesn't convention state that current is defined as the apparent movemnt of positive charge, in this case, in a direction opposite to what is shown in the graphic above? Am I even thinking about this correctly?? Thank you!