ImportanceSparse data exist regarding how clinician-assigned New York Heart Association (NYHA) class compares with heart failure (HF)–specific Kansas City Cardiomyopathy Questionnaire (KCCQ) in acute HF.ObjectiveTo compare concordance between NYHA class and KCCQ overall summary score (KCCQ-OS) in acute HF and investigate associations of changes in NYHA class and KCCQ-OS with long-term outcomes.Design, Setting, and ParticipantsIn this cohort study, patients with HF were enrolled from 52 hospitals in China between August 2016 and May 2018. Among patients with NYHA class and KCCQ-OS at admission and 1 month, levels of each scale were categorized into 4 groups from worst to best. Mild and moderate to severe discordance were defined as NYHA class and KCCQ-OS differing by 1 level or 2 or more levels, respectively. Multivariable models evaluated associations between improvements in the 2 measures and outcomes. Analysis was conducted from January to March 2023.ExposureChanges in NYHA class and KCCQ-OS from admission to 1 month.Main Outcomes and MeasuresAll-cause mortality, cardiovascular death, or first HF rehospitalization.ResultsA total of 2683 patients (1709 [63.7%] male; median [IQR] age, 66 [56-75] years) were included. NYHA class II, III, and IV were presented in 374 patients (13.9%), 1179 patients (44.0%), and 1130 patients (42.1%), respectively, and the median (IQR) KCCQ-OS was 44.4 (28.3-61.9). Concordance, mild discordance, and moderate to severe discordance between admission NYHA class and KCCQ-OS occurred in 954 patients (35.6%), 1203 patients (44.8%), and 526 patients (19.6%), respectively. For KCCQ-OS, kernel density overlaps were 73.6% between NYHA II and III, 63.8% between NYHA II and IV, and 88.3% between NYHA III and IV. Most patients experienced improvements in NYHA and KCCQ-OS from admission to 1 month. After adjustment, there was no significant association between improvements in NYHA class and 4-year all-cause mortality, whereas 5 or more point improvements in KCCQ-OS were independently associated with a lower risk of 4-year mortality (hazard ratio, 0.84; 95% CI, 0.74-0.96; P = .01). NYHA class and KCCQ-OS improvements were both associated with decreased risk of 1-year composite cardiovascular death or HF rehospitalization.Conclusions and RelevanceIn this cohort study of acute HF, discordance between NYHA class and KCCQ was common, and KCCQ was more relevant to subsequent mortality than NYHA class.