Abstract: The invention provides devices and methods for performing less-invasive surgical procedures within an organ or vessel. In an exemplary embodiment, the invention provides a method of closed-chest surgical intervention within an internal cavity of a patient's heart or great vessel. According to the method, the patient's heart is arrested and cardiopulmonary bypass is established. A scope extending through a percutaneous intercostal penetration in the patient's chest is used to view an internal portion of the patient's chest. An internal penetration is formed in a wall of the heart or great vessel using cutting means introduced through a percutaneous penetration in an intercostal space in the patient's chest. An interventional tool is then introduced, usually through a cannula positioned in a percutaneous intercostal penetration.