The press conference for 'Sound of Heart' took place on December 8!

SEE ALSO: Lee Kwang Soo returns to SBS entertainment program for the first time in two years

During this, Lee Kwang Soo made a promise for the drama's viewer ratings.  He said that if the ratings go over 10%, he would go on KBS 2TV's singing show 'National Singing Contest' with the cast members!

He said, "I expect it to go over 10% in viewer ratings and, for now, will start practicing [singing] with the other actors."