This study investigated the effects of two design principles as prescribed by the cognitive theory of multimedia learning on the situational interest of adult learners in a multimedia-based continuing education training program. One hundred and two adult learners employed by an emergency medical service were randomly assigned to one of three training groups designed to follow modality and redundancy design principles: animation-text, animation-narration, and animation-narration-text. A pretest was administered to participants in segments and presented to participants intermittently during the content in an attempt to reduce unintentional negative effects on interest, and a posttest was administered after participants submitted the self-reporting survey intended to measure situational interest in a multimedia-learning environment. An ANOVA was used to analyze the differences in situational interest between the groups, and independent t-tests were used to evaluate differences. The results of the study indicated that combinations of animation, narration, and text do influence the situational interest of learners. These results highlight the importance of carefully considering how to design multimedia environments for maximum impact on learners and specifically the implications of violating the "redundancy" design principle.