  Ultracold atomic gases have recently become a driving force in few-body
physics due to the observation of the Efimov effect. While initially observed
in equal mass systems, one expects even richer few-body physics in the
heteronuclear case. In previous experiments with ultracold mixtures of
potassium and rubidium, an unexpected non-universal behavior of Efimov
resonances was observed. In contrast, we measure the scattering length
dependent three-body recombination coefficient in ultracold heteronuclear
mixtures of $^{39}\mathrm{K}$-\87Rb and $^{41}\mathrm{K}$-\87Rb and do not
observe any signatures of Efimov resonances for accessible scattering lengths
in either mixture. Our results show good agreement with our theoretical model
for the scattering dependent three-body recombination coefficient and
reestablish universality across isotopic mixtures.
