One of the most numerous groups of idioms in Croatian and Slovak languages are somatic idioms that contain a body part as at least one of its components. The most numerous are idioms with body parts visible to the eye, however, somatism heart makes an exception. The word heart has many meanings. It is associated with a physical organ, a notion of the center, love, feelings, and emotions. The aim of this paper is to determine how much idioms with component heart coincide in both languages on a structural and conceptual level. For the purposes of this paper, a corpus of a total of 236 idioms, obtained from dictionaries and books, has been created. There are many similarities in Croatian and Slovak languages confirmed. The structural analysis found in both languages idioms-phonetic words, phraseological collocations, and idiomatic sentences, out of which phraseological collocations make the largest category. At the conceptual level, human-related idioms are the most common in both languages. However, in the Croatian language, more idioms describe human conditions and the results of one's own or others' actions, unlike the Slovak language, in which most of the idioms describe human characteristics, especially positive ones. In this paper, only a part of the idioms with component heart has been researched and only two analyzes have been processed, but due to the wide range of these idioms in both languages, it is crucial to conduct further research and analysis.