Objectives: In a single center experience, we retrospectively evaluated the short-term safety and efficacy of the TandemHeart® percutaneous transseptal left ventricular assist (PTVA®) system to deliver extracorporeal circulatory support during catheter based treatment of the unprotected left main coronary artery (ULMCA). Background: Percutaneous Coronary Intervention (PCI) of the ULMCA usually has been restricted to patients who are hemodynamically unstable or ineligible for coronary artery bypass grafting (CABG). High-risk patients for CABG should be considered at increased risk for PCI as well. In these patients the TandemHeart PTVA System (p-LVAD) may provide a valuable safeguard to reduce procedural risks. Methods and Results: Between July 2002 and May 2008 the TandemHeart was used in 9 very high risk patients (Logistic Euro score: 13.64 (7.46-29.67); Syntax score:43 (41-50); Mayo Clinic Risk score (MCRS) 7 (6-8); age: median 65 (range 55-71) undergoing elective PCI for the novo lesions on the ULMCA. All patients were declined for CABG by a heart team. A "true" percutaneous insertion technique was used in all patients, technical success rate was 100%. The median (range) time for implementation of circulatory support was 27 min (24-30). A median (range) pump flow up to 4.36 (3.40-5.54) L/min was achieved with significant reduction of left ventricular filling pressures, pulmonary capillary wedge pressure and a small increase of systemic arterial pressures. Median (range) duration of support was 93 min (50.4-102). Successful weaning was achieved in all patients. There was no in hospital death, survival at 6 months was (89%), whereas vascular access site complications were seen in 4 patients (44.4%). Conclusions: In very high risk PCI, assisted circulation using the TandemHeart-PTVA provides effective, total left ventricular support and may contribute to a reduced procedural risk and improved survival. The rate of device related cardiac and vascular complications was acceptable.