G-protein-coupled receptors are central to signal transduction and cell communication. The possibilitythat cells use receptor heteromerization to modulate individual receptor pathways is a surmise thatcannot be precluded. Given the complexity of these processes, mathematical models contribute tounderstanding how receptors and their respective ligands regulate signaling. Here, a mathematicalmodel is presented that quantifies the allosteric interactions within a receptor heterodimer. The model isbased on the operational model of allosterism including constitutive receptor activity, which providesthe pharmacological analysis of heteromerization with well-established and widely used modeling andfitting procedures.