In contrast, the presentation in regions with a low disease prevalence occurs more often in older pa- tients (age 50 to 70 years) who present decades after the initial rheumatic fever episode with calcified fibrotic leaf- lets in addition to commissural fusion and subvalvular involvement. Older patients with MS often have multiple other cardiac and noncardiac comorbidities, such as ath- erosclerotic disease, hypertension, and diastolic dysfunc- tion, all of which need to be taken into consideration in patient evaluation and management.1,2 Although most of MS in the world results from rheumat- ic heart disease, nonrheumatic calcific MS is found with in- creasing frequency in the elderly population in high-income countries Calcific MS is the result of calcification of the mi- tral annulus that extends into the leaflet bases, resulting in both narrowing of the annulus and rigidity of the leaflets.3 5 6.1. Stages of MS The stages of MS are defined by patient symptoms, valve anatomy, valve hemodynamics, and the consequences of valve obstruction on the left atrium (LA) and pulmo- nary circulation (Table 16). Rheumatic valve disease is the primary cause of MS, with anatomic features reflect- ing this disease process. Hemodynamic severity is best characterized by valve area, either directly planimetered by 2D or 3D imaging or calculated from the diastolic The definition of severe MS is based on the severity of symptoms, as well as the sever- ity at which intervention will improve symptoms. Thus, a mitral valve area 1.5 cm2 is considered severe, which typically corresponds to a transmitral mean gradient of >5 mmHg to 10 mmHg at a normal heart rate. How- ever, mean pressure gradient is highly dependent on transvalvular flow rate, the diastolic filling period, and heart rate. 