Objective To develop a framework for clinical practice guidelines that not only allows the representation of best practices, but also facilitates reasoning about acceptable alternatives for those best practices. Method Design of an explicit representation formalism of intentions of guidelines and guideline steps. Implementation of this representation and reasoning mechanisms in GASTON, a tool for representing and executing computerized clinical guidelines. Results The developed formalism is used to represent a heart failure clinical guideline. It is demonstrated that the representation of intentions provides the needed flexibility to avoid unnecessary errors and warnings. Conclusion By using an explicit representation of the intentions of guidelines and guideline steps, a flexible decision support system can be built that does not check only the adherence to the formal guideline but evaluates clinical activities in light of the intention of the guidelines.