Figurative idioms constitute a large proportion of multi-word expressions in everyday language. Contrary to the traditional view of idioms as non-compositional units, numerous studies in cognitive linguistics show that most idioms are not arbitrary but motivated by conceptual metaphors and metonymies that provide a link between literal and figurative meanings. Familiarity with particular source domains and conceptual mappings is regarded as a source of idiom transparency. In this article, we report on a study in which 85 Slovak students participated. Their task was to guess the meanings of English idioms containing three body parts: the eye, the hand and the heart. These body parts are not equally productive metaphorical source domains in English and Slovak. The research results which we present indicate that different prominence of the source domains in students’ mother tongue and the target language is one of the factors that influence idiom comprehension in a foreign language.