Myocardial T1 mapping is typically performed with three or more breath-holds, each covering one slice. This leads to patient discomfort and long exam times. Recently, simultaneous multi-slice/multi-band (SMS/MB) imaging was proposed to improve coverage and reduce scan time. It was shown that k-space interpolation outperformed SENSE-type reconstructions in terms of T1 precision. However, the slice-GRAPPA approach is a kernel estimation approach and does not allow for additional regularization. In this work, we sought to use a SPIRiT approach for improving SMS/MB myocardial T1 mapping by performing regularized multi-band reconstruction.