Does qt interval vary over the course of a day? had two ekgs done on same day - at different places - and both were normal, but different.

QT interval varies: with Heart Rate. The "corrected" QT interval tries to standardize this but there are a number of different correction formulas and the calculation for each EKG machine may have been resulted using different methods. The key is it is not abnormal. So worry not.

Variation: Since your heart is a dynamic organ, it works on demand and is affected by physical activities, emotional status, food intake (caffeine) etc . The heart rate , and amplitude may vary all day long. However, your QT interval should not vary much at all .