Previous studies in healthy humans have established that the (E850ml) volume enclosed by the pericardial sac is nearly constant over the cardiac cycle, exhibiting a transient E5% decrease (E40ml) from end-diastole to end-systole. This volume decrease manifests as a "crescent" at the ventricular free wall level when short-axis MRI images of the epicardial surface acquired at end-systole and end-diastole are superimposed. Based on the (near) constant-volume property of the four-chambered heart, the volume decrease ("crescent effect") must be restored during subsequent early diastolic filling via the left atrial conduit volume. Therefore, volume conservation-based modeling predicts that pulmonary venous (PV) Doppler D-wave volume must be causally related to the radial displacement of the epicardium () (i.e. magnitude of "crescent effect" in the radial direction). We measured from M-mode echocardiographic images and D-wave velocity-time integral (VTI) from Doppler PV flow of the right superior PV in 11 subjects with catheterization-determined normal physiology. In accordance with model prediction, high correlation was observed between and D-wave VTI (r = 0.86) and early D-wave VTI measured to peak D-wave velocity (r = 0.84). Furthermore, selected subjects with various pathological conditions had values of that differed significantly. These observations demonstrate the volume conservation-based causal relationship between radial pericardial displacement of the LV and the PV D-wave generated filling volume in healthy subjects as well as the potential role of the M-mode echo-derived radial epicardial displacement index as a regional (radial) parameter of diastolic function.