Abrupt onset and offset of acceleration induces hemodynamic changes that activate a number of reflex cardiovascular responses. At high +Gz on a centrifuge, apparently healthy subjects occasionally develop a serious cardiac arrhythmia such as supraventricular tachycardia or asystole. We report on four such cases and examine the effect of rapid centrifuge braking (1 G x s(-1)) on the arrhythmia. It appears that the hemodynamic consequences and reflex responses produced by rapid deceleration may have a positive effect on paroxysmal supraventricular tachycardia, slowing the heart rate or terminating the arrhythmia. On the other hand, deceleration tends to intensify sinus bradycardia. If further study confirms these findings, medical monitors and centrifuge operators may want to consider using gradual braking in cases of bradycardia.