[NOTE:FRAMES 37 AND 38 INTENTIONALLY OMITTED] Although these ECG findings are most often caused by mitral stenosis due to rheumatic heart disease, that diagnosis is becoming quite rare, at least in the United States, and other causes of obstruction (or stenosis) at the level of the mitral valve must be considered. These include an intracardiac tumor extending into the mitral valve orifice, usually a left atrial myxoma, or by extracardiac compression of the mitral valve ring by tumor or constrictive pericarditis.