Introduction: ischemic left bundle branch block (LBBB) is left coronary occlusion. We report an atypical case of de novo ischemic LBBB in relation to a tight right coronary lesion. Material and methods: Mr H, 53 years old with no modifiable risk factors, consulted for a typical angina pain evolving since 4 hours. The per-critical ECG showed a complete de novo LBBB with criteria of acute coronary ischemia. Coronary angiography showed a tight lesion of the right coronary artery that was stented with a good evolution marked by the regression of symptoms and signs of LBBB ischemia. Discussion: Ischemic LBBB is a coronary emergency requiring urgent coronary reperfusion. The diagnosis is facilitated by the commonly used Sgarbossa and Smith criteria. An occlusion of the anterior interventricular artery is most often incriminated. There is no evidence of a relationship with a right coronary lesion. The literature is poor in the description of the culprit lesions in ischemic LBBB.