The Japanese Air Self Defense Force has been conducting high-G training to enhance the +Gz tolerance of F-15 and F-4 fighter pilots since 1981. All the trainees have received ECG monitoring during the +Gz stress, both for safety and for medical evaluation. Various arrhythmias have been found previously, but most of the pilots who developed them were qualified for fighter aircraft because these arrhythmias were considered as non-hazardous for flight safety. Rarely, cases of aeromedically "serious" arrhythmias were observed with alteration of consciousness during the centrifuge ride. Three cases of sinoatrial block and one case of ventricular tachycardia were reviewed with their aeromedical dispositions. Imbalance of autonomic nerves induced by high +Gz is discussed as a possible etiology. The importance of ECG monitoring during centrifuge training is reemphasized as a means of medical evaluation of fighter pilots.