It means making decisions on emotion and intuition and/or doing what is best for you without worrying what other people think. In sayings and songs, 'heart' is often contrasted with 'head' "heart" = emotion, feelings, being true to yourself "head" = thinking, facts, intellect Happy new year to you too.

= his own heart. The heart of the man who's talking. The expressions sounds gay, but there you go.