Between the ventricles.
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in·ter·ven·tric·u·lar .int-ər-ven-'trik-yə-lər, -vən- adj situated between ventricles <an \interventricular septal defect>
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in·ter·ven·tric·u·lar (in″tər-vən-trikґu-lər) between ventricles.Medical dictionary. 2011.