Anticoagulant medications, particularly Vitamin K Antagonists (VKAs), are essential for managing thrombotic conditions but can cause severe side effects such as spontaneous hematomas. This case report describes a 69-year-old woman on VKA therapy who developed a large right breast hematoma. Immediate suspension of VKA, blood transfusions, and vitamin K administration led to clinical improvement. Breast ultrasonography confirmed the diagnosis, and after a week, the hematoma regressed, allowing for the resumption of anticoagulation with unfractionated heparin. This case highlights the need for careful monitoring and management of VKA therapy, especially in elderly patients.