The optimal therapy for numerous disease states involves the replenishment of intravascular volume. Unfortunately, our current clinical measures of volume status are imperfect. Given biologic plausibility and preliminary study, it is possible that static and/or dynamic measures of internal jugular vein (IJV) size may correlate with volume status and/or be associated with volume responsiveness. If so, this type of assessment might be a more ideal clinical volume-assessment tool. This pilot study aims to establish proof of concept via evaluation of this question in patients following cardiac surgery.