Beneath the endocardium.
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sub·en·do·car·di·al .səb-.en-dō-'kärd-ē-əl adj situated or occurring beneath the endocardium or between the endocardium and myocardium <\subendocardial blood loss>
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sub·en·do·car·di·al (sub″en-do-kahrґde-əl) beneath the endocardium.Medical dictionary. 2011.