Firstly, to compare gender-dependent differences of cardiac repolarization in both adult and young rabbits. Secondly, to analyze the effect of gonadectomy on these gender differences in cardiac repolarization. We evaluated potential gender differences in cardiac repolarization with both microelectrode and ECG recordings. QT(end), JT(end), and T(peak-end) intervals and action potential durations at 30%, 50% and 90% of full repolarization were used to assess ventricular repolarization in adult (normal and gonadectomized) and young rabbits of both sexes. Adult rabbits exhibited clear gender-related differences in repolarization evidenced by significantly longer JT(end) and T(peak-end) intervals and significantly longer APD30, APD50 and APD90 in females. These gender-related differences in repolarization were absent in young rabbits and were abolished by gonadectomy. Developmental changes of repolarization are present in rabbits. These changes are in agreement with those reported in humans and may further support the role played by sex hormones in the modulation of cardiac repolarization.