We observed MS 1054-0321, the highest redshift cluster of galaxies in the Einstein Medium Sensitivity Survey (EMSS), with the Chandra ACIS-S detector. We find the X-ray temperature of the cluster to be 10.4 +1.7 -1.5 keV, lower than, but statistically consistent with, the temperature inferred previously. This temperature agrees well with the observed velocity dispersion and that found from weak lensing. We are also able to make the first positive identification of an iron line in this cluster and find a value of 0.26 +/- 0.15 for the abundance relative to solar, consistent with early enrichment of the ICM. We confirm significant substructure in the form of two distinct clumps in the X-ray distribution. The eastern clump seems to coincide with the main cluster component. It has a temperature of 10.5 +3.4 -2.1 keV, approximately the same as the average spectral temperature for the whole cluster. The western clump is cooler, with a temperature of 6.7 +1.7 -1.2 and may be a subgroup falling into the cluster. Though the presence of substructure indicates that this cluster is not fully relaxed, cluster simulations suggest that we will underestimate the mass, and we can, therefore, use the mass to constrain Omega_m. From the overall cluster X-ray temperature we find the virial mass of the cluster to be at least 4.5 x 10^14 h^{-1} M_{odot}. We revisit the cosmological implications of the existence of such a hot, massive cluster at a relatively early epoch. Despite the lower temperature, we still find that the existence of this cluster constrains Omega_m to be less than one. If Omega_m = 1 and assuming Gaussian initial perturbations, we find the probability of observing MS 1054 in the EMSS is ~7 x 10^{-4}.
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