MBC's 'Heartstrings' recently revealed some fun still-cuts of Yonghwa and Park Shin Hye playing the role of 'master' and 'slave'. Park Shin Hye plays the role of 'Lee Kyu Won', a girl who agrees to play slave to Yonghwa's character, 'Lee Shin', for a month.�One of the first missions he gives her is to deliver a warm cappuccino to him every morning. Since it costs $2.80, he gives her $3, but she doesn't have the chance to return his change until he eventually catches on.�He orders her to pay him back with interest, and although she tries to work her aegyo on him, it's to no avail, as he makes her take out her emergency funds to pay him back. A representative said, "They're close friends who know a lot about each other so they work in a way that brings out the best in each other.�Viewers will be able to see a new change in their relationship as 'Lee Kyu Won' begins to develop her feelings towards the cold but lovable 'Lee Shin'." [gallery columns=4] Source + Photos: Star News via Naver