In most ECG leads, a normal Q wave is less than 0.04 second in duration and less than one third the amplitude of the R wave in that lead.

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With the exception of leads III and aVR, a normal Q wave in the limb leads is less than 0.04 second (one small box) in duration and less than one third the height of the R wave in that lead. An abnormal (pathologic) Q wave is more than 0.04 second in duration or more than one third the height of the following R wave in that lead. Myocardial infarction is one possible cause of abnormal Q waves.

In Most ECG Leads, a Normal Q Wave Is Less