The researchers recruited patients from a university referral hospital in northeastern Thailand. All patients had symptoms, such as difficulty with breathing, from severe mitral stenosis. The researchers used heart sonograms to identify the patients with a clot in their left atrium. They gave these patients blood thinners (by mouth) for 6 months. They regularly tested patients to make sure that their blood was not “too thin” and to guide appropriate doses of the medicine. After 6 months, patients received sonography again. Those with no evidence of clot on the second sonogram underwent PTMC.