[2014] 1.8.5 If pharmacological cardioversion has been agreed on clinical and resource grounds for new-onset atrial fibrillation, offer: a choice of flecainide or amiodarone to people with no evidence of structural or ischaemic heart disease or amiodarone to people with evidence of structural heart disease. [2014] 1.8.6 In people with atrial fibrillation in whom the duration of the arrhythmia is greater than 48 hours or uncertain and considered for long-term rhythm control, delay cardioversion until they have been maintained on therapeutic anticoagulation for a minimum of 3 weeks. During this period offer rate control as appropriate. [2006, amended 2014] 1.8.7 Do not offer magnesium or a calcium-channel blocker for pharmacological cardioversion. [2014] For a short explanation of why the committee made the 2021 recommendation and how it might affect practice, see the rationale and impact section on rate and rhythm control for people presenting acutely. Full details of the evidence and the committee's discussion are in evidence review I: non-ablative rate control therapies. Anticoagulation for people presenting acutely with atrial fibrillation 1.8.8 In people with new-onset atrial fibrillation who are receiving no, or subtherapeutic, anticoagulation therapy: in the absence of contraindications, offer heparin at initial presentation continue heparin until a full assessment has been made and appropriate antithrombotic therapy has been started, based on risk stratification (see section 1.2 on assessment of stroke and bleeding risks and section 1.6 on stroke prevention). 