Quantification of myocardial strains is essential for understanding cardiac mechanics. Previous techniques for assessing regional myocardial strains have been mainly limited to invasive procedures. A technique by which tagging can be added to magnetic resonance images (MRI) has recently been introduced and allows for noninvasive measurement of myocardial deformations. We have applied MRI tagging to two sets of orthogonal planes and have obtained three dimensional (3D) reconstructions of 24 myocardial cuboids at end-diastole (ED) and at end-systole (ES). Applying finite strain analysis to these cuboids we were able to study the longitudinal distribution of the endocardial and epicardial principal strains (PS) in the normal canine heart. In addition we have calculated the longitudinal distribution of the left ventricular (LV) transmural thickening using a 3D approach. Our results show similarity in the longitudinal distribution of endocardial PS and transmural thickening. These results imply that endocardial strains are determined not only by endocardial fiber deformations but mainly by geometrical coupling through transmural thickening.