Heat waves can have significant impacts on electricity supply and demand dynamics – increasing demand by amplifying the need for space cooling and decreasing supply via the thermal derating of transmission lines and power plant capacities. Future heat waves are expected to be more intense, more frequent, and more spatially widespread. In this study, we use a suite of coupled detailed sectoral models to explore how the changing characteristics of heat waves over the western United States (U.S.) influences the supply and demand dynamics of the U.S. Western Interconnection. The specific models we utilize include an electricity demand model that projects hourly electricity demand at the Balancing Authority (BA) scale in response to variations in weather, models of weather-sensitive solar and wind power generation, and a nodal production cost model that simulates the operations of the bulk electric grid. We test the hypothesis that the broader spatial extent of projected future heat waves will make heat-wave-driven peak demands more spatiotemporally coincident across BAs in the western U.S. Such a change would have implications for the capacity of the transmission grid to relieve grid stress during heat waves as the ability to import power from other BAs on the grid would be reduced. The meteorological forcing we utilize is based on 40-years (1980-2019) of historical heat waves that are then replayed twice into the future (2020-2099) under varying levels of warming. This approach allows us to examine how specific historical heat wave events and their resulting impacts on the grid may look in a warmer future climate. Results could help stakeholders and decision makers to make necessary preparations for prospective future extreme weather events.