1. Why this study? 1.1. Significance and difficulty of the problem being addressed. Aortic stenosis is the most encountered valvular disease According to the 2007 ESC guidelines (1), moderate aortic stenosis (AS) is defined as valve area 1.0-1.5 cm² (0.6 cm²/m² to 0.9 cm²/m² body surface area (BSA)) or mean aortic gradient of 30-50 mmHg in the presence of normal flow conditions. We already know how to treat patients with severe AS, symptomatic or not. On the contrary, in patients with moderate AS there is not a clear agreement on what to do to reduce the excess mortality (detailed below). Why do these patients die and what can we do to reduce mortality rates? 1.2. Originality of the proposed solution and the appropriateness of the objectives. There are already some progression factors in all spectrum of AS that have been highlighted (discussed below) and which could influence mortality in this patient subgroup, but none of the studies address exclusively to moderate AS. The majority of these studies have major limitations, are not prospective, and even if some are, the parameters followed do not cover the complete cardiological investigational tools (no 3D left ventricular (LV) ejection fraction (EF), no strain, no magnetic resonance imaging (MRI), etc.). As in any major disease, lots of studies that include moderate AS are contradictory on the same matter (see progression of AS). We aim to identify all clinical, biological, echo and imagistic parameters that predispose to increased progression rates in a prospective randomized trial which will include ONLY patients with moderate AS, with the investigational tools provided in 2012. Once those parameters are found, medical and interventional treatment could be implemented to decrease the mortality rates.