Penetrating wounds to the heart may present to the emergency unit with the presence of blood in the pericardial sac as determined on ultrasound. If these patients are stable, the study hypothesis is that they can be managed with a very simple surgical procedure called a subxyphoid pericardial window (SXW), in which the blood is drained from around the heart via a small skin incision below the rib cage. In all other centres in the world these cases are managed by open chest surgery called a sternotomy. The investigator's experience in dealing with these injuries is that this is unnecessary and requires a large amount of resources for no benefit to the patient.