In this paper we present a dynamic texture based motion segmentation approach to address the challenging problem of heart localization and segmentation in 4D Spatio-temporal cardiac images. Our approach introduces time-dependent dynamic constraints into model-based segmentation, and it has the advantage of producing segmentation results that are both spatially and temporally consistent. Compared to previous methods that segment cardiac contours, our method offers the following advantages: 1) the heart can be quickly localized in 4D cardiac images with distinct dynamic signatures; 2) heart dynamics are learned online and adaptively by analyzing the dynamic texture from the video sequence of a cardiac cycle and then incorporated in the segmentation process; and 3) the proposed dynamic features can be easily integrated with model-based segmentation methods. We illustrate our framework through combining the new dynamic constraints with active contour models, and demonstrate its performance on sequences of 4D MRI and tagged MRI images of the heart. We also validate the accuracy of the segmentation results by comparing with ground truth marked by experts.