As percutaneous coronary intervention (PCI) is being applied to higher-risk patients, ie, those with unprotected left main, multi-vessel disease, last remaining vessel, compromised left ventricular function, and ongoing ischemia, interventional cardiologists have used different percutaneous assist devices in an attempt to reduce procedure risk. The definition of high risk has varied among trials. There is no definitive evidence for superiority of the more invasive devices over the intra-aortic balloon pump (IABP); furthermore, a prophylactic strategy of IABP insertion has not proven superior to a provisional strategy. The purpose of this report is to review the physiologic mechanism of action of the devices and discuss indications, limitations, and clinical outcomes during high-risk PCI.