InclusionC riteria:  Eligible patients on the waiting list for radiofrequency ablation of Atrial Flutter at the Hammersmith Hospital, Imperial College Healthcare NHS Trust.  Suitable candidate for catheter mapping/ablation of arrhythmias. Eighteen (18) to eighty-five (85) years of age. Body Mass Index (BMI) <40 (Wt. in Kgs / Ht. in cm). Signed Informed Consent.  Exclusion Criteria:  Severe cerebrovascular disease Moderate to severe renal impairment (eGFR<30 ml/min/1.73m2) Active gastrointestinal bleeding. Active infection or fever. Short life expectancy. Significant anaemia. Severe uncontrolled systemic hypertension. Severe electrolyte imbalance. Ejection fraction <35%. Congestive heart failure (NYHA IV). Unstable angina requiring emergent PTCA (percutaneous transluminal coronary angioplasty) or CABG (Coronary Artery Bypass Grafting). Recent myocardial infarction. Bleeding or clotting disorders. Uncontrolled diabetes. Inability to receive IV or oral Anticoagulants. Unable to give informed consent (these patients would not be recruited). Previous catheter or surgical ablation treatment for Atrial Fibrillation. Previous catheter ablation treatment for Atrial Flutter. Pregnancy (urinary pregnancy test will be offered on the day of the procedure for all women of reproductive age) Drug and/or alcohol abuse. Patients who have participated in another study of an investigational medicinal product in the last 3 months.