A percutaneous left ventricular support (PLVS) system can play an important role in the short-term support of patients with severe heart failure, but these devices are not available for clinical use. We devised a new transseptal left atrial (LA) cannula for PLVS without thoracotomy. The cannula is 21 Fr in size (internal diameter: 5.3 mm) and 65 cm in length. This transseptal LA cannula can be inserted easily into the left atrium under fluoroscopy, by the usual transseptal technique, using a conventional Brockenbrough's needle. PLVS was used in two patients who developed cardiogenic shock following acute myocardial infarction and underwent resuscitation using percutaneous cardiopulmonary support (PCPS). The patients could not be weaned from PCPS even after successful percutaneous transluminal coronary angioplasty (PTCA), and PLVS provided 3.0 L/min of assist flow. The duration of PLVS was 114 and 92 hr. Both patients were weaned from PLVS, and one survived. There were no complications related to the PLVS. PLVS with a new transseptal LA cannula may be effective and useful for patients with severe heart failure.