Vitamin K antagonists (VKA) based oral anticoagulation, is widely used for the prevention and treatment of thromboembolic disease. The major complication of this therapy is bleeding, and sometimes it can occur in unsuspected areas. Spontaneous pectoral hematoma is one of the rare complications due to over anticoagulation by VKA therapy, with only a few cases reported in the literature. Concomitant use of this therapy with commonly used antibiotic, especially in the elderly with multiple comorbidities, can increase the risk of bleeding. Herein, we report a case of a 72-year-old woman under VKA for the treatment of atrial fibrillation, who presented with a spontaneous massive pectoral hematoma, while using antibiotic to treat a respiratory tract infection, who was successfully managed.