Traditionally, global and longitudinal (i.e., regional) left ventricular (LV) diastolic function (DF) assessment has utilized features of transmitral Doppler E- and A-waves or Doppler tissue imaging (DTI)-derived mitral annular E'- and A'-waves, respectively. To date, quantitation of regional DF has included M-mode-based approaches and strain and strain-rate imaging (in selected imaging planes), while analysis of mitral annular 'oscillations' has recently provided a new window into longitudinal (long-axis) function. The remaining major spatial degree of kinematic freedom during diastole, radial (short-axis) motion, has neither been fully characterized nor exploited for its potential to provide radial LV stiffness (k'_rad) and relaxation/damping (c'_rad) indexes. Prior characterization of regional (longitudinal) DF used only annular E'- and A'-wave peak velocities or, alternatively, myocardial strain and strain-rate. By kinematically modeling short-axis tissue motion as damped radial oscillation, a novel method of estimating k'_rad and c'_rad during early filling is presented. As required by the (near) constant-volume property of the heart and tissue/blood incompressibility, in subjects (n=10) with normal DF, we show that oscillation duration-determined longitudinal (k'_long, c'_long) and radial (k'_rad, c'_rad) parameters are highly correlated (R=0.69, R=0.92, respectively). Selected examples of diabetic and LVH subjects yield radial (k'_rad, c'_rad) parameters that differ substantially from controls. Results underscore the utility of the incompressibility-based causal relationship between DTI-determined mitral annular long-axis (longitudinal mode) and short-axis (radial mode) oscillations in healthy subjects. Selected pathologic examples provide mechanistic insight and illustrate the value and potential role of regional (longitudinal, radial) DF indexes in fully characterizing normal vs. impaired DF states.