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Normal Intervals and Durations

The normal adult heart rate ranges from 60/minute to 100/minute.

The P-R interval varies with age and with heart rate.  For adults, the normal range is from 0.14 to 0.21 seconds, the average being 0.17 seconds.
The QRS complex duration varies with age.   For adults, the average is 0.08 seconds, with an upper normal limit of 0.10 seconds.
The QT interval varies with age, sex, and heart rate.  The upper normal limit for an adult with a slow (60/min) normal heart rate is 0.43 seconds, the average being 0.39 seconds.   For an adult with a fast normal heart rate (100/min), the average is 0.31 seconds and the upper normal limit is 0.34 seconds.

For complete tabular data, please see:

        Hurst, et al, The Heart, 7th edition, 1990, McGraw-Hill
        Rushmer, Cardiovascular Dynamics, 4th edition, 1976, W. B. Saunders Company