The radial artery route is being increasingly used by interventional cardiologists as a default access site for both diagnostic and interventional coronary procedures, and although rare, serious complications can occur. We herein report a potentially catastrophic complication of radial percutaneous coronary intervention (PCI) in the form of a large mediastinal and retro-left-atrial hematoma from possible subclavian artery injury with tracheal compression and stridor in a 60-year-old female presenting with anteroseptal myocardial infarction having undergone PCI of the left anterior descending artery through right radial access and then planned for a second stage PCI of the right coronary artery. The patient was managed conservatively with close hemodynamic and echocardiographic monitoring, inotrope support, and blood transfusions. Transradial PCI, despite having a better safety profile in terms of bleeding compared to transfemoral PCI, is not without complications. Manipulation of hydrophilic guidewires as well as diagnostic catheters while performing radial procedures can cause injury to conduit vessels, potentially leading to intrathoracic, axillary, and arm hematomas may remain undetectable in the cath lab, presenting late and can pose a diagnostic and management challenge. Decision to proceed toward repeat interventional/surgical/"wait and watch" strategy should be guided by the patient's clinical status and noninvasive imaging.