하트 = "heart" - it usually means the heart shape (♥) which signifies "love" or support. 뿅 = onomatopoeia for something popping up or bubbling out of a liquid with a crisp sound. 뿅뿅 = such a thing repeating. So 하트 뿅뿅 is a very informal expression for "A lot of love", "I send my love", or something similar.