Atrial fibrillation (AF) is a pathological arrhythmia affecting performance horses and is termed paroxysmal (pAF) when self-terminating to sinus rhythm. Little is known about pAF as its sporadic nature makes it difficult to diagnose. Therefore, continuous electrocardiographic monitoring devices, such as implantable loop recorders (ILR), are necessary to detect the time of onset and episode duration. This case report presents the detection of pAF in a 9-year-old Warmblood horse after successful transvenous electrical cardioversion (TVEC). An ILR continuously monitored the heart rhythm over 28 months and detected 12 episodes of pAF of which two episodes were associated with reduced performance, while others occurred asymptomatically at rest. The estimated episode duration ranged from 6 min to 46.5 h. The antiarrhythmic drug sotalol (2 mg/kg bwt BID PO) was given prior to TVEC and then for 4 weeks. As episodes continued to occur, sotalol was prescribed for another 4 weeks, 6 months after TVEC. Continuous monitoring after TVEC allows for detection of AF recurrence and identification of AF burden, approximate time of onset and possible identification of trigger events. Early diagnosis and antiarrhythmic treatment may prevent a progression to persistent AF.