Atrial fibrillation (AF) is a common arrhythmia associated with poor outcomes. N-3 fatty acids have been shown to provide significant cardiovascular risk reduction, but they may exacerbate the risk of AF. The pathway by which N-3 fatty acids may be arrhythmogenic is unknown. One possible mechanism involves cardiac chamber morphology alteration. The purpose of this study was to investigate the effect of icosapent ethyl (IPE) on left atrial (LA) size and left ventricular (LV) mass. This study used coronary computed tomographic angiography images gathered from the Effect of Icosapent Ethyl on Progression of Coronary Atherosclerosis (EVAPORATE) trial. EVAPORATE was a randomised, double-blind, placebo-controlled study finding a significant reduction in coronary atherosclerosis progression in patients with residually elevated triglycerides despite statin therapy on 4 g IPE daily versus 4 g placebo daily. Computed tomography images were used to measure LA size and LV mass at 0 and 18 months. Of 80 enrolled patients, 68 were included in the final analysis. Baseline demographics and risk factors were similar between IPE and placebo cohorts. LA anterior- posterior diameter measured on axial (p=0.51) and sagittal (p=0.52) orientations were not different over time. Also, there was no difference between groups in the change in LA volume (p=0.84). Change in LV mass was similar between groups (p=0.13). In conclusion, this study did not detect differences in LA size or LV mass over 18 months between patients on 4 g daily IPE versus placebo., Competing Interests: Conflicts of interest MGR: Consultant for HeartFlow. DLB: Advisory boards for Boehringer Ingelheim, Cardax, CellProthera, Cereno Scientific, Elsevier Practice Update Cardiology, Janssen, Level Ex, Medscape Cardiology, MyoKardia, NirvaMed, Novo Nordisk, PhaseBio, PLx Pharma, Regado Biosciences, and Stasys; Board of Directors for Boston VA Research Institute, DRS.LINQ (stock options), Society of Cardiovascular Patient Care, and TobeSoft; Inaugural Chair, American Heart Association Quality Oversight Committee; Data Monitoring Committees: Acesion Pharma, Assistance Publique-Hôpitaux de Paris, Baim Institute for Clinical Research (formerly Harvard Clinical Research Institute, for the PORTICO trial, funded by St. Jude Medical, now Abbott), Boston Scientific (Chair, PEITHO trial), Cleveland Clinic (including for the ExCEED trial, funded by Edwards), Contego Medical (Chair, PERFORMANCE 2), Duke Clinical Research Institute, Mayo Clinic, Mount Sinai School of Medicine (for the ENVISAGE trial, funded by Daiichi Sankyo), Novartis, Population Health Research Institute; Honoraria: American College of Cardiology (Senior Associate Editor, Clinical Trials and News, ACC.org; Chair, ACC Accreditation Oversight Committee), Arnold and Porter law firm (work related to Sanofi/Bristol-Myers Squibb clopidogrel litigation), Baim Institute for Clinical Research (formerly Harvard Clinical Research Institute; RE-DUAL PCI clinical trial steering committee funded by Boehringer Ingelheim; AEGIS-II executive committee funded by CSL Behring), Belvoir Publications (Editor in Chief, Harvard Heart Letter), Canadian Medical and Surgical Knowledge Translation Research Group (clinical trial steering committees), Cowen and Company, Duke Clinical Research Institute (clinical trial steering committees, including for the PRONOUNCE trial, funded by Ferring Pharmaceuticals), HMP Global (Editor in Chief, Journal of Invasive Cardiology), Journal of the American College of Cardiology (Guest Editor; Associate Editor), K2P (Co-Chair, interdisciplinary curriculum), Level Ex, Medtelligence/ReachMD (CME steering committees), MJH Life Sciences, Piper Sandler, Population Health Research Institute (for the COMPASS operations committee, publications committee, steering committee, and USA national co-leader, funded by Bayer), Slack Publications (Chief Medical Editor, Cardiology Today’s Intervention), Society of Cardiovascular Patient Care (Secretary/Treasurer), WebMD (CME steering committees); Other: Clinical Cardiology (Deputy Editor), NCDR-ACTION Registry Steering Committee (Chair), VA CART Research and Publications Committee (Chair); Research Funding: Abbott, Afimmune, Aker Biomarine, Amarin, Amgen, AstraZeneca, Bayer, Beren, Boehringer Ingelheim, Bristol-Myers Squibb, Cardax, CellProthera, Cereno Scientific, Chiesi, CSL Behring, Eisai, Ethicon, Faraday Pharmaceuticals, Ferring Pharmaceuticals, Forest Laboratories, Fractyl, Garmin, HLS Therapeutics, Idorsia, Ironwood, Ischemix, Janssen, Javelin, Lexicon, Lilly, Medtronic, Moderna, MyoKardia, NirvaMed, Novartis, Novo Nordisk, Owkin, Pfizer, PhaseBio, PLx Pharma, Recardio, Regeneron, Reid Hoffman Foundation, Roche, Sanofi, Stasys, Synaptic, The Medicines Company, 89Bio; Royalties: Elsevier (Editor, Cardiovascular Intervention: A Companion to Braunwald’s Heart Disease); Site Co-Investigator: Abbott, Biotronik, Boston Scientific, CSI, St. Jude Medical (now Abbott), Philips, Svelte; Trustee: American College of Cardiology; Unfunded research: FlowCo, Merck, Takeda. MJB: Amarin grant support and speakers bureau, General electric grant support. SSK, SL, AK, SSM: None declared., (Copyright © 2023 Medinews (Cardiology) Limited.)