Carbohydrate antigen 125 (CA125) is a congestion and inflammation biomarker and has been proved to be related to a worse prognosis in heart diseases. However, the precise relationship between elevated CA125 in patients with ST-segment elevation myocardial infarction (STEMI) has not yet been sufficiently studied. We set out to determine the association of CA125 with all-cause mortality at 6 months in STEMI. CA125, N-terminal pro brain natriuretic peptide (NTproBNP) and high sensitive C-reactive protein (hs-CRP) were measured in 245 patients admitted consecutively with STEMI undergoing coronary angioplasty. The mean age in our sample was 63.7 years, 64.9% were males, 28.3% had diabetes and 17.7% presented with acute heart failure (Killip ≥ 2). The median serum level of CA125 was 8.1 U/ml. At 6 months, the rate of all-cause mortality was 18% (44 patients). Receiver operating characteristic curve analysis demonstrated that CA125 presented similar performance to predict mortality as NTproBNP and hs-CRP. Patients with CA125 ≥ 11.48 had a higher rate of mortality (Hazard Ratio = 2.07, 95% confidence interval = 1.13-3.77, p = 0.017) than patients with CA125 < 11.48. This study suggests that elevated CA125 levels might be used to identify patients with STEMI with a higher risk of death at 6 months. CA125 seems to be a similar predictor of mortality compared to NTproBNP and hs-CRP. Myocardial infarction with ST-segment elevation (STEMI) is a life-threatening disorder with high morbidity and mortality despite advances in treatment. Patients presenting with STEMI tend to be heterogeneous and immediate risk stratification at the time of presentation is essential for optimal management 1-4. Markers of congestion and inflammation, such as natriuretic peptides (NP) and high sensitive C-reactive protein (hs-CRP), have been shown to be prognostic markers. However, the biomarkers currently available are not perfect, and their correct interpretation requires careful consideration of the specific clinical scenario 5. Carbohydrate antigen 125 (CA125) is a congestion and inflammation biomarker. It has been studied in patients with heart diseases, especially heart failure 6. However, the precise relationship between elevated CA125 in patients with STEMI and cardiovascular events has not yet been sufficiently studied. This study set out to evaluate the relationship between CA125 and mortality in STEMI patients in comparison with N-Terminal pro brain natriuretic peptide (NTproBNP) and hs-CRP. Methods patients and study design. This was a prospective cohort at a single center. Patients consecutively admitted with STEMI undergoing primary angioplasty were included. The diagnosis of STEMI was made based on the third universal definition 7. Two hundred and seventy one patients were considered to be included. Patients were excluded if they had chronic heart failure (n = 3), previous coronary revascularization (n = 11), kidney failure (n = 8), absence of severe coronary disease (n = 4), end-stage liver disease, ongoing infection or malignancy.