Sung Si-kyung is releasing a new OST for the first time in three years. On December 4, he will drop With a Certain Heart, the main theme for JTBC's new weekend drama Waiting for Gyeongdo.

The song was crafted with the drama's protagonist Gyeongdo (played by Park Seo-joon) in mind, weaving Sung Si-kyung's signature emotional depth and delicate vocal expression. He participated not only as the vocalist but also as the composer and overall producer, ensuring a fully polished sound. Lyricist Shim Hyun-bo wrote the lyrics, with arrangers Gooreum and Jeon Jin-hee joining the project.

As the drama's central theme, With a Certain Heart captures the emotional flow of the story in a beautiful and weighty way. Sung Si-kyung's return to OST work follows a long list of hits, including "Hee-jae" from Scent of Love, "You Are My Spring" from Secret Garden, and "Every Moment of You" from My Love From the Star.

Waiting for Gyeongdo follows the intertwined romance of Gyeongdo and Ji-woo (Won Ji-an), who reunite under complicated circumstances — he as the subject of an affair scandal, she as the reporter who covered the story. The drama premieres on December 6 at 10:40 p.m.