As a medical professional with expertise in cardiology, I can provide you with information on the normal QT and QTc intervals on an ECG. The QT interval is a measure of the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle, which corresponds to the time between the initial depolarization and the completion of repolarization of the ventricles. The QTc, or corrected QT interval, is a version of the QT interval that has been adjusted to account for variations in the heart rate. Normal QTc values are typically considered to be within the range of 340 to 440 milliseconds for both men and women. However, some sources suggest that the upper limit for men is 440ms and for women is 460ms. A QTc greater than 500ms is associated with an increased risk of a potentially dangerous heart rhythm called torsades de pointes. If the QTc is less than 350ms, it is considered abnormally short. A useful guideline to remember is that a normal QT interval is generally less than half the duration of the preceding RR interval, which is the time between two successive Q waves. read more >>

Normal QTc values. QTc is prolonged if > 440ms in men or > 460ms in women. QTc > 500 is associated with increased risk of torsades de pointes. QTc is abnormally short if < 350ms. A useful rule of thumb is that a normal QT is less than half the preceding RR interval.read more >>