A method of controlling the conditional execution of elements and subsystems in a block diagram is disclosed. Data structures known as Execution Contexts are created and associated with individual block diagram elements and subsystems. The Execution Contexts allow execution of the associated element or subsystem upon satisfaction of a specified pre-condition. The Execution Contexts may be inherited by other elements and subsystems in the block diagram and propagated programmatically throughout the block diagram. The use of the Execution Contexts allows for efficient code generation and block diagram execution, as well as supporting modular design concepts.