We have previously demonstrated that both parasite genetic variability and host genetic background were important in determining the differential tissue distribution of the Col1.7G2 and JG T. cruzi monoclonal strains after artificial infections in mice. We observed that the JG strain was most prevalent in hearts of mouse lineages with the MHC haplotype H-2(d) (BALB/c and DBA2), while Col1.7G2 was predominant in hearts from C57BL/6 mice, which have the H-2(b) haplotype. To assess whether the MHC gene region indeed influenced tissue tropism of T. cruzi, we used the same two parasite strains to infect C57BL/6 (H-2(b)) and C57BLKS/J (H-2(d)) mice; the latter strain results from the introgression of DBA2 MHC region into the C57BL/6 background. We also performed ex vivo infections of cardiac explants from four congenic mice lineages with the H-2(b) and H-2(d) haplotypes arranged in two different genetic backgrounds: C57BLKS/J (H-2(d)) versus C57BL/6 (H-2(b)) and BALB/c (H-2(d)) versus BALB/B10-H2(b) (H-2(b)). In agreement with our former observations, Col1.7G2 was predominant in hearts from C57BL/6 mice (H-2(b)), but we observed a clear predominance of the JG strain in hearts from C57BLKS/J animals (H-2(d)). In the ex vivo experiments Col1.7G2 also prevailed in explants from H-2(b) animals while no predominance of any of the strains was observed in H-2(d) mice explants, regardless of the genetic background. These observations clearly demonstrate that the MHC region influences the differential tissue distribution pattern of infecting T. cruzi strains, which by its turn may be in a human infection the determinant for the clinical forms of the Chagas disease.