  We use an effective-field-theory framework to analyze the Efimov effect in
heteronuclear three-body systems consisting of two species of atoms with a
large interspecies scattering length. In the leading-order description of this
theory, various three-body observables in heteronuclear mixtures can be
universally parameterized by one three-body parameter. We present the
next-to-leading corrections, which include the effects of the finite
interspecies effective range and the finite intraspecies scattering length, to
various three-body observables. We show that only one additional three-body
parameter is required to render the theory predictive at this order. By
including the effective range and intraspecies scattering length corrections,
we derive a set of universal relations that connect the different Efimov
features near the interspecies Feshbach resonance. Furthermore, we show that
these relations can be interpreted in terms of the running of the three-body
counterterms that naturally emerge from proper renormalization. Finally, we
make predictions for recombination observables of a number of atomic systems
that are of experimental interest.
