  We introduce a heterogeneous version of a contagious McKean--Vlasov system
whose heterogeneity has a natural and particularly tractable structure. It is
shown that this system characterises the limit points of a finite particle
system with applications to solvency contagion in interbank models and coupled
integrate-and-fire models in mathematical neuroscience. Furthermore, we provide
a result on global uniqueness for the full common noise system under a simple
smallness condition on the strength of interactions, and we show that there is
a unique differentiable solution up to an explosion time in the system without
common noise.
