Patients undergoing percutaneous coronary intervention (PCI) with severely compromised left ventricular systolic function and complex coronary lesions, including multivessel disease, left main disease, or bypass graft disease, are at higher risk of adverse outcomes from hemodynamic collapse. The TandemHeart percutaneous ventricular assist device may provide circulatory support during high-risk PCI. We implanted the TandemHeart device in eight patients who underwent high-risk PCI. The patients were considered to be at exceptionally high risk for decompensation due to procedural complexity combined with underlying LV dysfunction. The mean ejection fraction was 30% +/- 9% and five patients were turned down for surgical revascularization. Seven patients underwent multivessel PCI, including three patients who underwent unprotected left main coronary artery PCI. There was 100% procedural success. The TandemHeart was removed immediately post-PCI with no groin complications. Six patients are event- and symptom-free at 189 +/- 130 days; one patient died 10 days post-PCI after lower extremity bypass surgery and another developed acute renal failure postprocedure, requiring hemodialysis. Our initial clinical experience with the TandemHeart ventricular assist device demonstrates that hemodynamic support can be rapidly achieved percutaneously during high-risk PCI, with excellent procedural success in highly complex and critically ill patients.