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Figure 4 Description of 3-dimensional myocardial strain in the radial/circumferential/longitudinal (rcl) system. Interpretation of myocardial strain (i.e., deformation) depends on the coordinate system used. For clinical purposes, description of strain in the rcl system is preferable. Radial strain (R) indicates deformation of the heart in the radial direction. Positive radial strain during systole reflects the local contribution of the myocardium to wall thickening. Circumferential strain (C) reflects intramural circumferential shortening. A negative value is related to myocyte contraction. Longitudinal strain (l) reflects the regional longitudinal shortening from base to apex.