Introduction: The incidence of cardiac arrhythmia is approximately 1% in the neonatal period and 1–3% in late pregnancy. Atrial flutter (AF), a rhythm disorder based on the mechanism of reentry, represents approximately 32% of all neonatal cardiac arrhythmias. In the majority of cases, the flutter is converted to sinus rhythm using antiarrhythmic drugs, transesophageal overdrive pacing, or synchronized electrical cardioversion. Case presentation: We present a case of a born on term, female infant who was noted to be tachycardic on the fetal monitor. Clinical examination revealed tachypnea and tachycardia with dysrhythmia, at a heart rate of 250 bpm. Electrocardiography showed AF with 2–3 : 1 atrioventricular conduction (atrial and ventricular rates were 350 bpm and 250–275 bpm, respectively). Echocardiography revealed no relevant structural disease. Therapy with amiodarone and prophylactic anticoagulant was initiated. As no control of ventricular rate was obtained and a succession of three ventricular extrasystoles was noted on the surface ECG, propranolol therapy was initiated, without success. Therefore, synchronized electrical cardioversion was applied, with conversion to sinus rhythm at a heart rate of 136 bpm. The neonate was discharged in good condition. Conclusions: AF is one of the most common high ventricular rate arrhythmias during fetal age. Uncontrolled AF may precipitate heart failure, and prompt restoration to sinus rhythm may require electrical cardioversion in cases refractory to anti-arrhythmic drugs, in order to prevent possible complications.