Studies have shown that the quality of chest compressions for cardiac arrest decreases markedly after only a brief time. This is thought to be an important contributor to an adverse outcome of resuscitation, which has led to recommendations to alternate chest compression providers. This study compared alternating rescuers every 1 min versus every 2 min in a manikin simulation. Forty pairs of rescuers were randomly assigned to either scenario. The main outcome measure was the number of effective compressions. The results were analysed using one-way analysis of variance. Over the full 8 min, no significant difference was found in the number of effective chest compressions (p=0.707). Furthermore, no significant difference was found when comparing each 2 min block. An explanation for this may be that the compressions lost due to fatigue in the 2 min scenario are approximately offset by compressions lost due to the practicalities of changing over. Power calculations with these results show that an unfeasibly large number of scenarios would be needed to definitively demonstrate the superiority of one of the scenarios. It seems reasonable to alternate chest compression providers every 2 min, to prevent the loss of effective compressions due to fatigue and to minimise interruptions of chest compressions. The ideal time to do this would be during the rhythm and pulse check as dictated by current guidelines.