OBJECTIVES: To assess the cost-effectiveness of TAVI compared with standard therapy consisting mainly of balloon aortic valvuloplasty (BAV) in patients with severe aortic stenosis who are ineligible for conventional aortic valve replacement (AVR) from the perspective of the Ontario health care payer.  METHODS: A microsimulation decision analytical model was developed to estimate the incremental costs and benefits associated with both interventions over a lifetime time horizon.  Monthly adverse event and patient mortality rates were determined using data from the PARTNER randomized control trial (cohort B).  Quality of life values were determined through literature review, expert opinion, and data provided by the PARTNER investigators.  The London Health Sciences Centre Case Costing Initiative and the Canadian Institute for Health Administration (CIHI) were used to estimate costs.  Extensive sensitivity analyses were performed to explore the impact of uncertainty surrounding model parameters on the resultant cost-effectiveness estimates.  The primary outcome measure was the incremental cost-effectiveness ratio (ICER) with benefits expressed as quality-adjusted life years (QALYs).  Costs were expressed in 2011 CAD$.  Both costs and benefits were discounted at 5%. RESULTS: The base case ICER was approximately $38,448 per QALY gained.  The results of the sensitivity analyses yielded ICERs ranging from approximately $32,238/QALY to $43,887/QALY.  ICER estimates were most sensitive to changes in the cost of the Edwards SapienTMDevice. CONCLUSIONS: At cost-effectiveness thresholds normally used to define value for money in health care, TAVI represents a cost-effective treatment option for patients with severe aortic stenosis who are currently ineligible to undergo conventional aortic valve replacement in the province of Ontario.