What is the normal QT interval upper limit for males and females?

• A. Less than 0.60 seconds in both sexes
• B. Normal: Less than 0.47 seconds in males and less than 0.48 seconds in females
• C. Less than 0.50 seconds in both sexes
• D. Less than 0.40 seconds in males and 0.42 in females

Answer: (B)

The QT interval tracks how long the ventricles take to depolarize and then repolarize, and it’s influenced by heart rate and sex. Clinically we use sex-specific upper limits because females tend to have a slightly longer QT interval.

The commonly used normal upper limits are about 0.47 seconds for men and 0.48 seconds for women. So this reflects the natural difference between the sexes and provides a threshold to flag potential prolongation that could raise the risk of certain arrhythmias.

Other options set values that are either far too long, ignore the sex difference, or are unrealistically short for normal ranges, which is why they’re not the best choice.