BACKGROUND: Myocardial injury after noncardiac surgery (MINS) is associated with 30-day mortality in heterogeneous surgical populations but is barely described after acute high-risk abdominal surgery. The impact of dynamic changes has not previously been investigated. The objectives were to determine the incidence of MINS in this population, the association between mortality and MINS, and whether plasma troponin I (TnI) dynamics have any impact on mortality. METHODS: A prospective cohort study of 341 patients undergoing acute high-risk gastrointestinal surgery was conducted. Plasma TnI was measured at the first four postoperative days. MINS was defined as any increased TnI level >59 ng/L. TnI dynamic required either two succeeding measurements of TnI >59 ng/L with a >20% increase/fall or one measurement of TnI >59 ng/L with a succeeding measurement of TnI <59 ng/L with a >50% decrease. Adjusted mortality rates were calculated using inverse probability of treatment weighting and competing risk analyses. RESULTS: The incidence of MINS was 23.8% and dynamic TnI changes occurred in 15.6% of the patients. The unadjusted 30-day and 1-year mortality were 19.8% and 35.9% in patients with MINS, compared with 2.7% and 11.6%, respectively, in patients without MINS (p < 0.001). After adjusting, the differences remained significant. There was no difference in mortality between patients with or without dynamic changes in TnI level. CONCLUSION: MINS occurred frequently and was associated with increased mortality. TnI monitoring might help identify patients with increased risk of mortality and improve care. Research on preventive measures and treatments is warranted. TRIAL REGISTRATION NUMBER AND AGENCY: ClinicalTrials.gov Identifier: NCT05933837, retrospective registered.