Pericardiocentesis is a definitive strategy to remove pericardial effusion. In this report, we present a rare case of a 23-year-old man with sudden delayed hemorrhagic shock due to branch bleeding of the left internal thoracic artery (LITA) two days after undergoing pericardiocentesis. Angiography, embolization, and drainage were effective. As far as we know, this is the first report that shows delayed bleeding due to branch injury of the LITA as a possible complication after pericardiocentesis.