Right ventricular systolic dysfunction (RVsD) frequently occurs in patients with ST-elevation myocardial infarction (STEMI). However, the diagnosis depends on the echocardiographic parameters to define RVsD. The right ventricle longitudinal shortening fraction (RV-LSF) is an accurate and reproducible 2-dimensional speckle-tracking parameter associated with clinical events in various pathologies. This study aimed to evaluate the association between RVsD and major adverse cardiovascular event (MACE) occurrence in a cohort of patients with STEMI. Adult patients with STEMI admitted to Amiens University Hospital's cardiovascular intensive care unit between May 2021 and November 2022 who underwent coronary angiography and transthoracic echocardiography within 48 hours of admission were included. RVsD was defined as RV-LSF <20%. The primary outcome was MACE occurrence, including heart failure, myocardial infarction, stroke, and death within 6 months of admission. A multivariable Cox regression analysis with proportional hazard ratio models assessed the association between RVsD and MACEs. In the 164 included patients, 72 (44%) had RVsD and 92 (56%) did not. The RVsD group had a significantly higher proportion of MACEs during the 6-month follow-up (n = 23 of 72, 33%) than the group without RVsD (n = 8 of 92, 9%, p = 0.001). RVsD showed an independent association with MACEs at 6 months (hazard ratio 3.1, 95% confidence interval [CI] 1.35 to 7.30, p = 0.008). Left ventricular ejection fraction <40% and Thrombolysis in Myocardial Infarction score >4 were independently associated with RVsD (odds ratio 2.80, 95% CI 1.34 to 5.98 and odds ratio 2.15, 95% CI 1.18 to 4.39, respectively, p = 0.015). The cumulative risk of MACEs at 6 months was 33% for RV-LSF <20% and 9% for RV-LSF ≥20% (log-rank test p <0.001). RVsD, defined by RV-LSF <20%, is associated with an increased risk of MACEs after STEMI.