People are usually awake during the procedure, but doctors may give a drug to help them relax. People are closely monitored during PCI because balloon inflation momentarily blocks blood flow in the affected coronary artery. This blockage can cause chest pain and changes in the heart’s electrical activity (detected by ECG) in some people. Fewer than 1% of people die during PCI, and fewer than 5% have nonfatal heart attacks. Coronary artery bypass surgery becomes necessary immediately after PCI for 1% or fewer of people.