Before PCI, patients with allergies to contrast dye (the solution injected into the blood vessels so that blockages show up on x-ray) should receive medications (prednisone [steroids] and diphenhydramine [Benadryl, Pfizer, New York, New York]) to prevent allergic reactions. Patients need plenty of fluid before and after PCI to decrease the chances that the dye will damage the kidneys. During the procedure, blood clots can form at the site of the blockage that is being treated. Aspirin and other medications that make the platelets in the body less “sticky” help to decrease this complication. Doctors should use symptoms, electrocardiography (ECG), and blood tests to monitor patients for signs of complications during the procedure. They should also be alert for signs of internal bleeding, which can include a drop in blood count or blood pressure or pain in the groin, flank, abdomen, or back. Tenderness or a lump in the groin, or an abnormal sound heard through a stethoscope placed over the groin, may indicate that the small puncture in the artery in the groin made during the PCI procedure has not healed properly (pseudoaneurysm or arteriovenous fistula). About 5 to 10 of every 100 patients who undergo PCI will show some sign of heart damage if this is carefully screened for. However, most of the time, this heart damage is very small, and patients experience no symptoms. Less common complications of PCI include stroke and the need for emergency surgery. Fewer than 1 out of every 100 patients who have PCI die as a result of a PCI complication. After the procedure, physicians should prescribe drugs (aspirin and clopidogrel [Plavix, Bristol-Myers Products, New York, New York]) to prevent a blood clot from forming at the site in the heart where the coronary stent was placed.