The heart man is an olive-green fish dressed in a heart costume used to entertain little kids and he only appears in the episode "Valentine's Day." Heart man appears at the Valentine's Day Carnival.
He is shaped like a huge bright red heart with a big smile on his face. The fish inside of the suit is shown to have olive green fins.
The heart man was seen in "Valentine's Day" with a group of children at a carnival. Patrick, who was upset at not receiving any special gifts scared the children away and tore the heart costume into two, revealing a fish inside.
[Heart man does not have any lines himself, but Patrick has a famous line in heart man's scene]
Patrick: I defy you, heart man! [rips heart man's costume off, leaving him in his Valentine boxers]