Background: Functional mitral regurgitation induces adverse effects on the left ventricle and the left atrium. Left atrial (LA) dilatation and reduced LA strain are associated with poor outcomes in heart failure (HF). Transcatheter edge-to-edge repair (TEER) of the mitral valve reduces heart failure hospitalization (HFH) and all-cause death in selected HF patients., Objectives: The aim of this study was to evaluate the impact of LA strain improvement 6 months after TEER on the outcomes of patients enrolled in the COAPT (Cardiovascular Outcomes Assessment of the MitraClip Percutaneous Therapy for Heart Failure Patients With Functional Mitral Regurgitation) trial., Methods: The difference in LA strain between baseline and the 6-month follow-up was calculated. Patients with at least a 15% improvement in LA strain were labeled as "LA strain improvers." All-cause death and HFH were assessed between the 6- and 24-month follow-up., Results: Among 347 patients (mean age 71 ± 12 years, 63% male), 106 (30.5%) showed improvement of LA strain at the 6-month follow-up (64 [60.4%] from the TEER + guideline-directed medical therapy [GDMT] group and 42 [39.6%] from the GDMT alone group). An improvement in LA strain was significantly associated with a reduction in the composite of death or HFH between the 6-month and 24-month follow-up, with a similar risk reduction in both treatment arms (P interaction = 0.27). In multivariable analyses, LA strain improvement remained independently associated with a lower risk of the primary composite endpoint both as a continuous variable (adjusted HR: 0.94 [95% CI: 0.89-1.00]; P = 0.03) and as a dichotomous variable (adjusted HR: 0.49 [95% CI: 0.27-0.89]; P = 0.02). The best outcomes were observed in patients treated with TEER in whom LA strain improved., Conclusions: In symptomatic HF patients with severe mitral regurgitation, improved LA strain at the 6-month follow-up is associated with subsequently lower rates of the composite endpoint of all-cause mortality or HFH, both after TEER and GDMT alone. (Cardiovascular Outcomes Assessment of the MitraClip Percutaneous Therapy for Heart Failure Patients With Functional Mitral Regurgitation [COAPT]; NCT01626079)., Competing Interests: Funding Support and Author Disclosures The COAPT trial was sponsored by Abbott. Dr Delgado received speaker fees from Abbott Vascular, Edwards Lifesciences, Merck Sharp and Dohme, and GE Healthcare. Dr Stassen has received funding from the European Society of Cardiology (European Society of Cardiology Training Grant App000064741). Dr Weissman is associate director of an academic echocardiography core laboratory (MedStar Health Research Institute) with institutional contracts with Abbott, Neovasc, Ancora, Mitralign, Medtronic, Boston Scientific, Edwards Lifesciences, Biotronik, and Livanova. Dr Grayburn has received grant support from Abbott Vascular, Medtronic, Boston Scientific, Cardiovalve, Edwards Lifesciences, W. L. Gore, Medtronic, and NeoChord; and has received consulting fees from Abbott Vascular, Edwards Lifesciences, W. L. Gore, and 4C Medical. Dr Kar has received consulting fees and is an Advisory Board member at Boston Scientific; has received consulting fees and stock equity from Valcare; and has received consulting fees from W.L. Gore and Medtronic. Dr Lim has received research grant support from Abbott, Boston Scientific, Edwards, and Medtronic; has received consultant fees from LagonaTech, Valgen, and Venus; and is an Advisory Board member for Ancora and Philips. Dr Lindenfeld has received research grant support from AstraZeneca; and has received consulting fees from Abbott Vascular, CVRx, Edwards Lifesciences, RESMED, Relypsa, Boehringer Ingelheim, and V-Wave. Dr Abraham has received research grant support from the National Heart, Lung, and Blood Institute (National Institutes of Health 1 UG3/UH3 HL140144-01, 08/01/18-07/31/22, “Impact of Low Flow Nocturnal Oxygen Therapy on Hospital Readmission/Mortality in Patients with Heart Failure and Central Sleep Apnea [LOFT-HF]”); has received consulting income from Abbott Vascular, Boehringer-Ingelheim, and Zoll Respicardia; has received speaker honoraria from Impulse Dynamics; and has received salary support from V-Wave Medical. Dr Mack has served as coprimary investigator for the PARTNER Trial for Edwards Lifesciences and COAPT trial for Abbott; and has served as study chair for the APOLLO trial for Medtronic. Dr Asch is the Director of the Core Laboratories at MedStar Health Research Institute, which has institutional contracts (no personal compensation) with Abbott, Neovasc, Ancora, Mitralign, Medtronic, Boston Scientific, Edwards Lifesciences, Biotronik, and Livanova. Dr Stone has received speaker honoraria from Medtronic, Pulnovo, and Infraredx; has served as a consultant to Valfix, TherOx, Robocath, HeartFlow, Ablative Solutions, Vectorious, Miracor, Neovasc, Abiomed, Ancora, Elucid Bio, Occlutech, CorFlow, Apollo Therapeutics, Impulse Dynamics, Cardiomech, Gore, Amgen, Adona Medical, and Millennia Biopharma; and has equity/options from Ancora, Cagent, Applied Therapeutics, Biostar family of funds, SpectraWave, Orchestra Biomed, Aria, Cardiac Success, Valfix, and Xenter. Dr Stone’s daughter is an employee at Medtronic; and Dr Stone’s employer, Mount Sinai Hospital, has received research support from Abbott, Abiomed, Bioventrix, Cardiovascular Systems Inc, Phillips, Biosense-Webster, Shockwave, Vascular Dynamics, Pulnovo, and V-wave. Dr Bax has received speaker fees from Abbott Vascular. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)