Abstract Background In individuals with suspected acute coronary syndrome (ACS), serial assessments of high-sensitivity cardiac troponin-T (hsTnT) levels demonstrate associations with both short- and long-term mortality and recurrent ischemic events. Nonetheless, the relationship with subsequent heart failure remains inadequately characterized. Purpose We investigated the association between single and serial hsTnT levels and subsequent hospitalization or outpatient medical encounters related to heart failure in individuals presenting with suspected ACS. Methods Utilizing Danish national registries from 2012 to 2019, we identified individuals without known heart failure who underwent dual hsTnT assessments ( 99th percentile upper reference limit: 13.5 ng/l), spaced 1-7 hours apart during hospitalization for myocardial infarction (MI), unstable angina, observation for suspected MI, or chest pain. Participants were categorized based on their hsTnT concentration patterns from the first to the second measurement (primary groups: normal, rising, persistently elevated, or falling) and the extent of hsTnT concentration alterations (secondary groups: <20%, >20 to 50%, or >50% in either direction). Additionally, they were grouped into quartiles based on the initial hsTnT measurement (<=9 ng/l, 10-15 ng/l, 16-66 ng/l, >=67 ng/l) to assess whether heightened hsTnT concentrations correlated with an increased risk of heart failure. Standardized risks of hospitalization or outpatient contacts for heart failure were computed using multivariable logistic regression with average treatment effect modeling. Results The study encompassed 26,835 individuals, of whom 38.9% received discharge diagnoses of MI, 5.1% were diagnosed with unstable angina, and 56.1% with observation for suspected MI or chest pain. Median age was 64.2 years, with 59.5% males. Prevalence of known cardiovascular disease included coronary disease in 18.1% of cases, prior revascularization in 7.2%, atrial fibrillation or flutter in 7.9%, and a history of stroke in 6.3%. Within the initial 30 days, 628 persons received a heart failure diagnosis, with an additional 960 diagnosed between days 31-365. Subjects displaying two normal hsTnT values exhibited the lowest standardized absolute risk (0.39% in days 0-30; 0.58% in days 31-365), while those with persistently elevated concentrations demonstrated the highest risk (6.45% in days 0-30; 7.05% in days 31-365) (Figure). Notably, the magnitude of hsTnT within each primary group did not affect heart failure risk. Conversely, heart failure risk exhibited a positive association with hsTnT concentrations measured in the initial sample. Conclusions In individuals presenting with suspected ACS, subjects with a sustained elevation in hsTnT levels showed the highest risk of subsequent heart failure events. Moreover, a dose-response association was observed between hsTnT concentrations and heart failure risk.Figure