Sometimes a coronary angiogram reveals a narrowing that appears to be of intermediate severity and it may not be clear if that narrowing is causing an obstruction to the flow of blood. In a pressure wire study, a special wire with a pressure transducer in the tip is passed through the narrowing and a drug may be given to maximize blood flow through the artery. The pressure at the tip of the wire is then compared to the patient’s blood pressure to see if there is a significant difference. If the narrowing is obstructing blood flow a coronary stent can be implanted straight away using the pressure wire as a guide.