Although gender differences in resting corrected QT intervals have been well documented, the effects of age and exercise on gender differences in QT have not been well characterized. Data were analyzed from 91 healthy volunteers (47 women). Forty-five young subjects (aged 20 to 39 years) and 46 older subjects (61 to 84 years) were recruited. All underwent Bruce protocol stress testing. QT offset and QT peak were measured at exercise stages and during recovery. In a heart rate (HR)-independent analysis, data were divided into HR bins of 10 beats/min. In a HR-dependent analysis, 6 models were used to approximate the QT-RR relation; the best were used to analyze age and gender effects. Women had longer QT intervals than men at a HR < 100 beats/min for QT offset and < 110 beats/min for QT peak. At faster HRs, no significant differences were found. Older subjects had slightly longer QT intervals than the younger group, with a mean difference of 2 ms for QT offset and 9 ms for QT peak. Women had increased constant and slope coefficients. The QT increase in the elderly was relatively small. Gender differences in QT disappear at faster HRs, whereas age differences are smaller but are present throughout exercise, with no significant age-gender interaction. A natural logarithmic model provides the best approximation of the QT-RR relation with exercise, is simple to implement, and should become the preferred method of QT correction.