The embryonic heart and vascular bed interact dynamically to support rapid growth of the embryo during cardiovascular development. Pressure-volume relations define ventricular function during alterations in loading conditions. We analyzed these relationships in the embryonic heart in order to define ventricular function and the response of the ventricle and vascular bed to acute changes in preload. We simultaneously measured ventricular pressure and recorded 60 video images per second in n≥6 stage 16, 18 and 21 white Leghorn chick embryos at baseline and during the infusion of 1–2 microliters of physiologic buffer into the venous sinus (sinus venosus). Ventricular tetany was then induced with the topical application of 2 Molar sodium chloride. Video fields were traced for ventricular pressure and epicardial cross-sectional area. Cross-sectional area was converted to volume assuming ellipsoid geometry, and cavity volume was calculated as total volume minus wall volume derived from the tetanized heart. We defined end-diastole at the onset of ventricular contraction and end-systole at maximum pressure/volume ratio. Stroke volume increased linearly with end-diastolic volume. End-diastolic pressure-volume relations were positive and linear, and end-systolic pressure-volume relations were curvilinear downward. Arterial elastance decreased with growth of the embryo and with volume infusion. Pressure-volume loop area, an index of consumption of energy, doubled between the embryonic stages. Thus, embryonic ventricular pressure-volume relations define diastolic and systolic function at rest and in response to altered preload.
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