In a percutaneous coronary intervention, a doctor threads a flexible tube into one of the patient's blood vessels, usually one in the upper thigh. The doctor threads the tube up to the blocked blood vessels in the heart. On the end of the tube is a balloon. The doctor blows up the balloon, which pushes the plaque and blood clot against the side of the blocked blood vessel. This allows blood to flow through that blood vessel again. Sometimes, a doctor might also place a small mesh tube called a stent into the blood vessel. The stent will make sure the blood vessel stays open and does not get blocked again in the future.