Which of the following accurately represents a normal PR interval?
Measured from the beginning of the P to the beginning of the Q or R, and normal is 3 to 5 little boxes.
Measured from the end of the P to the beginning of the Q, and normal is 3 to 5 little boxes.
Measured from the beginning of the P to the beginning of the R, and normal is 0.04 to 0.12 seconds.
Measured from the end of the P to the beginning of the R, and normal is 0.12 to 0.20 seconds.