The conventional dynamic cardiac phantom used in the field of nuclear medicine has a structure for which the size of the external side of the heart (the outer membrane substituting the myocardial layer) is fixed and only the inner side (the inner membrane substituting the ventricle part) moves anteroposteriorly. Therefore, its usefulness in technical evaluation is limited. Hence, we developed a new dynamic cardiac phantom in which the outer and inner membranes freely move. Methods: Using a SPECT/CT system, we performed validation by filling the myocardial layer of the dynamic cardiac phantom with solution and the ventricle part with contrast medium. We evaluated myocardial wall motions of 3 segments (basal, mid, and apical) by setting the stroke ratios at 20:20 and 10:10 (ventricle-to-myocardial layer ratio). Results: The myocardial wall motions (mean ± SD) at the stroke ratio of 20:20 were 7.50 ± 0.44, 11.15 ± 0.56, and 9.90 ± 0.24 mm in the basal, mid, and apical segments, respectively. The wall motions (mean ± SD) at the stroke ratio of 10:10 were 3.82 ± 0.43, 5.63 ± 0.39, and 4.53 ± 0.10 mm, respectively. Conclusion: In our dynamic cardiac phantom, different movements could be induced in the myocardial wall by freely changing the stroke ratio. These results suggest that the use of this phantom can realize technical evaluation that presumes various clinical conditions.