Embedded systems are often composed from components of very different natures, e.g., mechanical and electronic. Composition of heterogeneous components is generally not well-defined, making design and verification difficult. Denotational mathematical frameworks for reasoning effectively on heterogeneous composition have recently been made available. In this work, we propose an operational version of this formalism, based on tag machines, that can represent heterogeneous composition, and we provide conditions under which the heterogeneous composition can be captured soundly and completely. We have implemented our operational framework in a prototype tool which we use for experimental evaluation.