Amiodarone and beta blockers are common treatments for new-onset atrial fibrillation (NOAF) in patients treated on an intensive care unit (ICU). How these treatments affect patients’ haemodynamic status is unclear, yet purported differences often affect clinicians’ treatment choice. We undertook a multicentre observational study of ICUs in one United States of America (USA) centre and two United Kingdom (UK) centres to explore the changes in blood pressure and cardiovascular support associated with amiodarone or beta blocker therapy for NOAF. We identified 2017 patients who developed NOAF during their ICU stay, of which 958 were treated with amiodarone or beta blockers as first line therapy. Neither amiodarone nor beta blockers were associated with significant changes in blood pressure over the 3h post-treatment initiation (amiodarone mean blood pressure (MBP +0.04mmHg/h, p = 0.90 and systolic blood pressure (SBP) +0.11mmHg/h, p = 0.83; beta blocker MBP -0.41mmHg/h, p = 0.17 and SBP -0.15mmHg/h, p = 0.75). Amiodarone was associated with a very slight increase in vasoactive medication use. In a subgroup of patients with lower blood pressures, amiodarone was associated with a slight improvement in blood pressure (+1.36mmHg/h, p = 0.02), whereas beta blocker therapy was not associated with any change (+0.24mmHg/h, p = 0.72). These data do not support the commonly held belief that beta blockers result in hypotension or increased vasoactive medication requirements when used for NOAF treatment within an ICU. These findings from observational data need investigating in well-designed randomised trials.