Background: Complete revascularization in ST elevation myocardial infarction (STEMI) patients with multivessel disease has resulted in reduction in composite clinical endpoints in medium sized trials. Only one trial showed an effect on hard clinical endpoints, but the revascularization procedure was guided by angiographic evaluation of stenosis severity. Consequently, it is not clear how Fractional Flow Reserve (FFR)-guided percutaneous coronary intervention (PCI) affects hard clinical endpoints in STEMI. Methods and Results: The Ffr-gUidance for compLete non-cuLprit REVASCularization (FULL REVASC) – is a pragmatic, multicenter, international, registry-based randomized clinical trial designed to evaluate whether a strategy of FFR-guided complete revascularization of non-culprit lesions, reduces the combined primary endpoint of total mortality, non-fatal MI and unplanned revascularization. 1,545 patients were randomized to receive FFR-guided PCI during the index hospitalization or initial conservative management of non-culprit lesions. We found that in angiographically severe non-culprit lesions of 90-99% severity, 1 in 5 of these lesions were re-classified as non-flow limiting by FFR. Considering lesions of intermediate severity (70%-89%), half were re-classified as non-flow limiting by FFR. The study is event driven for an estimated follow-up of at least 2.75 years to detect a 9.9%/year>7.425%/year difference (HR = 0.74 at 80% power (α = .05)) for the combined primary endpoint. Conclusion: This large randomized clinical trial is designed and powered to evaluate the effect of complete revascularization with FFR-guided PCI during index hospitalization on total mortality, non-fatal MI and unplanned revascularization following primary PCI in STEMI patients with multivessel disease. Enrollment completed in September 2019 and follow-up is ongoing.