### Key points The mitral valve separates the left atrium from the left ventricle (LV) and, as such, is an integral part of the high-pressure systemic circulation. Therefore, any pathology of the valve can have critical physiological effects that the anaesthetist must be aware of. Anaesthesia alters the way in which the heart, valve, and circulation interact and control of these changes needs to be both understood and anticipated. The mitral valve is a complex structure that incorporates not only the two main leaflets, but an annulus, tendinous cords, and papillary muscles connecting the valve leaflets to the LV (Fig. 1). Fig 1 The mitral valve and surrounding structures. The valve is in the ‘surgeon's view’ orientation with the heart tilted to the left. (a) AC, anterior commissure; PC, posterior commissure. (b) The mitral valve leaflets, each of which usually consists of three discrete segments or scallops. These are designated A1, A2, and A3 for the anterior leaflet and P1, P2, and P3 for the posterior leaflet. (c) Primary chordae are attached to the free edge of the valve leaflet, and secondary chordae are attached to the ventricular surface of the leaflet. (From)1. Reprinted with permission from Massachusetts Medical Society. ### Annulus The mitral valve's annulus is a saddle-shaped structure which is shaped more like a ‘D’ than an ‘O’. The aortic valve is wedged into the straight side of the ‘D’ and there is a fibrous continuity between the two valves. This means that one …