Background <p>Sinus node dysfunction can occur in patients with acute coronary syndrome (ACS), particularly in inferior myocardial infarction. Because the sinoatrial nodal artery (SANa) shows considerable anatomical variation, ischemia-related sinus arrest may occur depending on the origin and course of the artery. We report a case of sinus arrest associated with distal right coronary artery occlusion involving a rare SANa origin from the posterolateral branch.</p> Case presentation <p>A 59-year-old man presented with chest discomfort and marked bradycardia. Electrocardiography demonstrated sinus arrest with a junctional escape rhythm at 45 beats/min accompanied by ST-segment elevation in the inferior leads. Emergency coronary angiography revealed total occlusion of the distal right coronary artery at the posterolateral branch. The atrioventricular nodal artery was patent, and the SANa was not visualized initially. After guidewire crossing during primary percutaneous coronary intervention, a large SANa arising from the posterolateral branch became visible distal to the occlusion. Sinus rhythm was immediately restored following reperfusion. A drug-eluting stent was successfully deployed, and the patient had an uneventful clinical course without recurrence of bradyarrhythmia.</p> Conclusion <p>This case illustrates that distal right coronary artery occlusion may cause sinus arrest when a rare variant of the sinoatrial nodal artery arises from the posterolateral branch. Recognition of coronary anatomical variations is important when evaluating severe bradyarrhythmia in patients with ACS.</p>