Several observational studies have suggested that mortality and major complications after high-risk percutaneous coronary intervention (PCI) can be reduced by elective insertion of an intra-aortic balloon pump (IABP). However, to date, this assertion has never been tested in a randomized trial, and as such, international guidelines do not provide formal recommendations for IABP use in this setting. The BCIS-1 is a randomized trial that addresses the hypothesis that elective IABP insertion before high-risk PCI will reduce major adverse cardiac and cerebrovascular events (MACCEs) at hospital discharge or 28 days after index PCI, whichever occurs sooner. High risk is defined by the presence of severe left ventricular dysfunction as well as a large amount of myocardium at risk. Patients who are in cardiogenic shock, have a class I indication for IABP use, or have an absolute contraindication to IABP use will be excluded. Three hundred eligible patients will be randomized to receive elective IABP insertion or no planned IABP insertion. The findings of BCIS-1 are expected to define the role of balloon counterpulsation in high-risk PCI. Confirmation of the efficacy of elective IABP use may prompt review of the international guidelines, which are currently very restricted. In contrast, a neutral or adverse outcome with elective counterpulsation in these high-risk patients will allow evidence-based rationalization of the current disparity between guidelines and the frequent real-world use of elective IABP support.