One larger study comparing mixed rate control and rhythm control with a potassium-channel blocker (amiodarone) with or without rate control suggested little difference between the 2 groups. Based on this evidence and their experience, the committee decided that rhythm control could be considered but that the evidence no longer supported the stronger recommendation included in the 2014 guideline. The committee noted that postoperative atrial fibrillation often resolves naturally, meaning that rate control rather than rhythm control may be a suitable option for some people. Reducing the emphasis on rhythm-control strategies will allow rate-control strategies to be considered if appropriate for the person. The committee were also aware of the risk of adverse events if amiodarone, a rhythm control drug, is taken long-term. They highlighted that if a rhythm-control strategy is chosen, the need for rhythm control drugs should be reassessed at approximately 6 weeks, in line with current practice, and they should not be continued automatically for long periods of time. The committee agreed that 6 weeks is an appropriate time point to assess the person's recovery, including for example prosthetic valve function, and to check if sinus rhythm has been restored. The committee did not make a separate recommendation for people with pre-existing atrial fibrillation because of a lack of evidence. The committee noted that most people undergoing mitral valve surgery with pre-existing atrial fibrillation would undergo left atrial surgery to treat atrial fibrillation at the same time. How the recommendations might affect practice Rhythm control for the treatment of new-onset atrial fibrillation after cardiothoracic surgery is current practice and amiodarone is most commonly used. This can still be considered, but there may be a reduction in the use of rhythm control in this population and an increase in the use of rate-control drugs instead. 