Final answer:
A normal Q wave in an ECG is less than 0.04 sec in duration and less than one-third the height of the R wave in that lead. An abnormal Q wave is longer in duration and taller than one-third the height of the following R wave in that lead.
Step-by-step explanation:
In an ECG, it is important to differentiate normal (physiologic) Q waves from pathologic Q waves. A normal Q wave in the limb leads is less than 0.04 sec (one small box) in duration and less than one-third the height of the R wave in that lead. On the other hand, an abnormal (pathologic) Q wave is more than 0.04 sec in duration and more than one-third the height of the following R wave in that lead.