Final answer:
The normal PR interval on an ECG is between 3 to 5 little boxes, each representing 0.04 seconds, indicating the time from atrial to ventricular depolarization.
Step-by-step explanation:
The normal PR interval on an Electrocardiogram (ECG) reading is generally between 3 to 5 little boxes, each box representing 0.04 seconds. Therefore, the correct answer is b) Between 3 to 5 little boxes. The PR interval indicates the time period from the onset of atrial depolarization (P wave) to the start of ventricular depolarization (QRS complex). An abnormally long PR interval can suggest a first-degree AV block, indicating a delay in the conduction of electrical impulses between the atria and ventricles. In contrast, a short PR interval may be indicative of conditions where the electrical impulse bypasses part of the normal conduction pathway, such as in Wolff-Parkinson-White syndrome. Other segments and intervals like the QT interval, QRS complex, and ST segments provide additional information about the electrical activity of the heart.