This paper investigates the issue of how emotions such as disgust influence students' self-efficacy belief in terms of mastering a dissection task and also how these affect their interest in the biology of the heart. Following models of intrinsic motivation and the development of motivation, we expected disgust to negatively impact on students' self-efficacy belief and their interest levels. Ninety-two secondary school students completed questionnaires on disgust, self-efficacy belief and interest before and during the dissection of a pig's heart. We compared two groups of students, one that felt disgusted during dissection and one that did not. No differences in self-efficacy belief and interest were shown between the two groups before the dissection. The development of self-efficacy belief and interest proved to be significantly affected by the disgust experienced during dissection. During dissection, disgusted students saw themselves as less effective at mastering the dissection and reported lower interest in the heart than students who did not feel that emotion. These findings suggest that teachers should try to reduce disgust-provoking stimuli during dissection, since self-efficacy and interest can influence cognitive as well as motivational and affective processes. (Contains 2 figures.)