This thesis presents a system for generating dynamic facial expressions synchronized with speech, rendered using a tridimensional realistic face. Dynamic facial expressions are those temporal-based facial expressions semanti- cally related with emotions, speech and affective inputs that can modify a facial animation behavior. The thesis defines an emotion model for speech virtual actors, named VeeM (Virtual emotion-to-expression Model ), which is based on a revision of the emotional wheel of Plutchik model. The VeeM introduces the emotional hypercube concept in the R4 canonical space to combine pure emotions and create new derived emotions. In order to validate VeeM, it has been developed an authoring and player facial animation tool, named DynaFeX (Dynamic Facial eXpression), where a speech processing is realized to allow the phoneme and viseme synchronization. The tool allows either the definition and refinement of emotions for each frame, or group of frames, as the facial animation edition using a high-level approach based on animation scripts. The tool player controls the animation presentation synchronizing the speech and emotional features with the virtual character performance. DynaFeX is built over a tridimensional polygonal mesh, compliant with MPEG-4 facial animation standard, what favors tool interoperability with other facial animation systems.