There is limited knowledge on the occurrence of new-onset, transient atrial fibrillation during acute coronary syndromes; compared with patients in sinus rhythm, patients with paroxysmal atrial fibrillation have an increased risk of in-hospital and long-term recurrence of the arrhythmia, all-cause mortality and ischemic stroke. There is a lack of prospective, randomized studies on anticoagulant therapy modalities in this specific subset of patients. In the absence of a widely accepted anticoagulation algorithm, the international guidelines for the management of atrial fibrillation recommend to initiate anticoagulant treatment during acute coronary syndromes estimating in each patient the thrombotic and bleeding risk using the CHA2DS2-VASc and HAS-BLED scores, respectively. In the last updates of the guidelines for the management of atrial fibrillation, non-vitamin K oral anticoagulants are recommended over warfarin and, in patients with atrial fibrillation who have undergone percutaneous coronary intervention with stenting for acute coronary syndromes, dual antiplatelet therapy with rivaroxaban or dabigatran and clopidogrel is reasonable to reduce the risk of bleeding compared with triple therapy. Neither scientific evidences nor recommendations from the guidelines are available about the duration of anticoagulant therapy in case of paroxysmal atrial fibrillation during acute coronary syndromes.