To determine the optimum configuration of a 64-channel array coil for highly accelerated in vivo cardiac diffusion-weighted imaging (DWI), the encoding capability and sensitivity of three 64-channel arrays were designed, constructed, and evaluated. Simultaneous multi-slice (SMS) acceleration enabled enhanced efficiency of the diffusion acquisitions. The array configuration with a non-uniformly distributed loop density showed the most favorable cardiac imaging performance in both SNR and SMS encoding power. Cardiac DWI of a healthy volunteer mirrors the findings from phantom evaluation and testing. Such technically advanced coils are an important component for translation of cardiac DWI to clinical settings.