BACKGROUND: Periodontitis has been associated with coronary artery disease, but the impact of a periodontal treatment on the endothelial function of patients with a recent ST-segment elevation myocardial infarction (STEMI) was not investigated. METHODS: Randomized controlled trial (NCT02543502). Patients admitted between August 2012 and January 2015 were included. Patients were screened during the index hospitalization for STEMI, and those with severe periodontal disease were randomized 2 weeks later to periodontal treatment or to control. The primary endpoint of this trial was the between group difference in the variation of flow-mediated vasodilation (FMD) in the brachial artery assessed by ultrasound from baseline to the 6-month follow-up. Secondary outcomes were cardiovascular events, adverse effects of periodontal treatment and inflammatory markers. RESULTS: Baseline characteristics were balanced between patients in the intervention (n = 24) and control groups (n = 24). There was a significant FMD improvement in the intervention group (3.05%; p = .01), but not in the control group (-0.29%; p = .79) (p = .03 for the intergroup comparison). Periodontal treatment was not associated with any adverse events and the inflammatory profile and cardiovascular events were not significantly different between both groups. CONCLUSIONS: Treatment of periodontal disease improves the endothelial function of patients with a recent myocardial infarction, without adverse clinical events. Larger trials are needed to assess the benefit of periodontal treatment on clinical outcomes. CLINICAL TRIAL REGISTRATION: NCT02543502 (https://clinicaltrials.gov/ct2/show/NCT02543502?term=NCT02543502&rank=1).