PurposeThree 64‐channel cardiac coils with different detector array configurations were designed and constructed to evaluate acceleration capabilities in simultaneous multislice (SMS) imaging for 3T cardiac MRI.MethodsThree 64‐channel coil array configurations obtained from a simulation‐guided design approach were constructed and systematically evaluated regarding their encoding capabilities for accelerated SMS cardiac acquisitions at 3T. Array configuration A_Uni‐sized consists of uniformly distributed equally sized loops in an overlapped arrangement, B_Gapped uses a gapped array design with symmetrically distributed equally sized loops, and C_Dense has non‐uniform loop density and size, where smaller elements were centered over the heart and larger elements were placed surrounding the target region. To isolate the anatomic variation from differences in the coil configurations, all three array coils were built with identical semi‐adjustable housing segments. The arrays’ performance was compared using bench‐level measurements and imaging performance tests, including signal‐to‐noise ratio (SNR) maps, array element noise correlation, and SMS acceleration capabilities. Additionally, all cardiac array coils were evaluated on a healthy volunteer.ResultsThe array configuration C_Dense with the non‐uniformly distributed loop density showed the best overall cardiac imaging performance in both SNR and SMS encoding power, when compared to the other constructed arrays. The diffusion weighted cardiac acquisitions on a healthy volunteer support the favorable accelerated SNR performance of this array configuration.ConclusionOur results indicate that optimized highly parallel cardiac arrays, such as the 64‐channel coil with a non‐uniform loop size and density improve highly accelerated SMS cardiac MRI in comparison to symmetrically distributed loop array designs.