Simultaneous multislice (SMS) acquisition can be used to decrease the time between acquisition of fMRI volumes, which can increase sensitivity by facilitating the removal of higher-frequency artifacts and boosting effective sample size. The technique requires an additional processing step in which the slices are separated, or unaliased, to recover the whole brain volume. Full field of view images are reconstructed in k-space from multiband slices using kernels estimated with complex-valued least squares (slice-GRAPPA) or constrained complex-valued least squares (split slice-GRAPPA), where the constraints reduce signal leaking into aliased locations. SMS can lead to noise amplification, which decreases the benefits. We conduct a simulation study in k-space with complex-valued measurement errors to examine the impacts of SMS and reconstruction method. We also examined data from the Human Connectome Project and found evidence of slice leakage and noise amplification.