Thirty-one healthy subjects, aged 35 +/- 6 (21 to 48) years, were included in the study to evaluate the effect of ice water immersion on QT dispersion. There was no difference in the age between females (n = 11) and males (n = 20). Baseline, stress (at the end of ice water immersion, 4 degrees C, for 3 minutes) and recovery 12-lead electrocardiograms (ECGs) were recorded on each subject. During the test, a significant variability developed in both the QT dispersion (52 +/- 17, 68 +/- 25 and 59 +/- 21 ms; p = 0.015) and the corrected QT dispersion (56 +/- 17, 76 +/- 27 and 64 +/- 23 ms; p = 0.005), but not in the heart rate (74 +/- 11, 76 +/- 9, and 74 +/- 9 bpm, respectively; p = 0.447). There was no inter-sex difference in the baseline heart rate or QT dispersion, or in their response to ice water immersion. Age significantly correlated with the variation of QT dispersion to ice water immersion (r = 0.380, p = 0.035). With 37 years of age as a separation point, the variation of QT dispersion to ice water immersion was more obvious in the older group (28 +/- 22 vs. 10 +/- 19 ms, p = 0.023). In conclusion, cold may increase QT dispersion in healthy subjects, with a more obvious effect in the older ones.