Diagnostic Testing: Routine Follow-Up Rheumatic MS is a slowly progressive disease, char- acterized by a prolonged latent phase between the initial rheumatic illness and the development of valve The latent phase is an interval typically measured in decades in high-income countries but in considerably shorter periods in low- to middle-in- come countries, likely because of recurrent carditis. Once mild stenosis has developed, further narrow- ing is slow (decrease in valve area of 0.1 cm2 per year on average), although the rate of progression is highly variable.3 Importantly, progressive enlarge- ment of the RV and a rise in RV systolic pressure can be observed, even in the absence of a decrease in mitral valve area. Accordingly, repeat TTE at intervals dictated by valve area is an important aspect of dis- ease management, even in patients without symp- toms (Table 4). 6.2.1.4. Diagnostic Testing: Cardiac Catheterization In the contemporary era, assessment of MS and associ- ated lesions can be obtained in most patients by TTE, occasionally supplemented by TEE. However, there will be a subset of patients with nondiagnostic studies or for whom there is discordance between the clinical and echocardiographic findings. In older patients, other fac- tors contributing to symptoms may need to be further sorted out, such as concomitant diastolic dysfunction, LA noncompliance, or intrinsic pulmonary vascular dis- ease. Cardiac catheterization is useful in these patients to further characterize rheumatic MS hemodynamics and etiology of symptoms, as it can measure absolute pressures in the LV, LA, and pulmonary circulation at rest and with exercise. 