Background: Slow heart rate recovery (HRR) after exercise is associated with autonomic dysfunction and increased mortality. What HRR criterion at 1-minute after a 6-minute walk test (6MWT) best defines pulmonary impairment?., Study Design and Methods: A total of 5008 phase 2 COPDGene (NCT00608764) participants with smoking history were included. A total of 2127 had COPD and, of these, 385 were followed-up 5-years later. Lung surgery, transplant, bronchiectasis, atrial fibrillation, heart failure and pacemakers were exclusionary. HR was measured from pulse oximetry at end-walk and after 1-min seated recovery. A receiver operator characteristic (ROC) identified optimal HRR cut-off. Generalized linear regression determined HRR association with spirometry, chest CT, symptoms and exacerbations., Results: HRR after 6MWT (bt/min) was categorized in quintiles: ≤5 (23.0% of participants), 6-10 (20.7%), 11-15 (18.9%), 16-22 (18.5%) and ≥23 (18.9%). Compared to HRR≤5, HRR≥11 was associated with (p<0.001): lower pre-walk HR and 1-min post HR; greater end-walk HR; greater 6MWD; greater FEV 1 %pred; lower airway wall area and wall thickness. HRR was positively associated with FEV 1 %pred and negatively associated with airway wall thickness. An optimal HRR ≤10 bt/min yielded an area under the ROC curve of 0.62 (95% CI 0.58-0.66) for identifying FEV 1 <30%pred. HRR≥11 bt/min was the lowest HRR associated with consistently less impairment in 6MWT, spirometry and CT variables. In COPD, HRR≤10 bt/min was associated with (p<0.001): ≥2 exacerbations in the previous year (OR=1.76[1.33-2.34]); CAT≥10 (OR=1.42[1.18-1.71]); mMRC≥2 (OR=1.42[1.19-1.69]); GOLD 4 (OR=1.98[1.44-2.73]) and GOLD D (OR=1.51[1.18-1.95]). HRR≤10 bt/min was predicted COPD exacerbations at 5-year follow-up (RR=1.83[1.07-3.12], P=0.027)., Conclusion: HRR≤10 bt/min after 6MWT in COPD is associated with more severe expiratory flow limitation, airway wall thickening, worse dyspnoea and quality of life, and future exacerbations, suggesting that an abnormal HRR≤10 bt/min after a 6MWT may be used in a comprehensive assessment in COPD for risk of severity, symptoms and future exacerbations., Competing Interests: Summary conflict of interest statements: The authors report funding from the NIH in direct support of this work; other support, including consultancy, advisory board fees and contracted research from industry is outside the submitted work. A full list of disclosures is provided. Dongxing Zhao has no disclosures to report. Asghar Abbasi is supported by a postdoctoral fellowship from the Tobacco-Related Disease Research Program (28FT-0017). Richard Casaburi reports personal fees from Glaxo Smith Kline, Boehringer Ingelheim, Astra Zeneca, Regeneron and Genentech and contracted clinical research support from Astra Zeneca, Boehringer Ingelheim, Glaxo Smith Kline, Genentech and Regeneron outside the submitted work. Alessandra Adami is supported by a grant from NIH/NHLBI (R01HL151452). Nicholas B. Tiller is supported by a postdoctoral fellowship from the Tobacco-Related Disease Research Program (T31FT1692). Wei Yuan has no disclosures to report. Christopher Yee has no disclosures to report. Nicholas Jendzjowsky reports grant funding from AazeinTx, outside the submitted work; is a Parker B Francis Fellowship Recipient; reports US provisional patent, application no. 59263173-179 outside the submitted work; has patent 62/534,638 pending to University of Calgary. David MacDonald has no disclosures to report. Ken Kunisaki reports grants from NIH, during the conduct of the study, personal fees from Nuvaira for data safety and monitoring board services, and contracted clinical research support from Sanofi outside the submitted work. William Stringer reports research funding from AstraZeneca and consultancy for GlaxoSmithKline outside the submitted work. Janos Porszasz reports contracted clinical research support with United Therapeutics, Genentech and Regeneron outside the submitted work. Barry Make reports (related to the general topic of COPD over the last three years) grants from NHLBI, Pearl Research, Circassia, GlaxoSmithKline and AstraZeneca; advisory board fees from GlaxoSmithKline, AstraZeneca, Boehringer Ingelheim, Verona, Third Pole, and Phillips; consulting fees from AstraZeneca; medical board member, grants, non-financial support, grant funds provided to and controlled by National Jewish Health for/from Astra Zeneca, grants and CME activity for/from Glaxo Smith Kline, CME activity for Wolters Kluwer Health, Spiration, CME activity for Sunovion, Mt Sinai, Web MD, National Jewish Health, Novartis, American College of Chest Physicians, Projects in Knowledge, Hybrid Communications, Medscape, Ultimate Medical Academy, Eastern Pulmonary Society, Catamount Medical, Eastern VA Medical Center, and Academy Continued Health Care Learning, grants from Pearl Research (funds provided to and controlled by National Jewish Health), medical advisory board for Verona, Boehringer Ingelheim, Theravance, Phillips, and Science 24/7, non-financial support from Circassia, personal fees from Third Pole and Takeda, and grants from NHLBI, outside the submitted work. Russ Bowler has no disclosures to report. Harry Rossiter is supported by grants from NIH (R01HL151452, P50HD098593, R01DK122767, P2CHD086851) and the Tobacco Related Disease Research Program (T31IP1666). He reports consulting fees from Omniox Inc., and is involved in contracted clinical research with Boehringer Ingelheim, GlaxoSmithKline, Novartis, AstraZeneca, Astellas, United Therapeutics, Genentech and Regeneron. The authors report no other potential conflicts of interest for this work., (© 2021 Zhao et al.)