We describe an efficient approach to the registration problem of ultrasonic cardiac images using an affine transformation model, incorporating a mutual information based error minimisation. The affine motion model provides an analytic solution which has fast and stable convergence. The geometric and intensity constancy constraint is combined with the smoothness constraint, which allow us to have approximate image alignment. Due to complexity of a realistic motion, we then minimise the error in intensity between the registered source and the target image in the context of mutual information. In fact, image registration can be reached when the amount of information buried in the images is maximised. The experimental results demonstrate that this hybrid framework is highly efficient in registering different cardiac images.