Verification and validation tasks, as applied to software specifications, enable early detection of analysis and design flaws prior to implementation. Several fault injection techniques for software Verification and validtion are proposed at the code level.In this work, we address verification and validation analysis methods based on fault injection at the software specification level. We present a fault model and a fault injection process for UML dynamic specifications. We use a case study based on a cardiac pacemaker for illustrating the developed approach.