Suits those in 13 across on open sea (6)

I believe the answer is:

hearts

I'm a little stuck... Click here to teach me more about this clue!

'suits' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Maybe you can see an association between them that I don't see?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for hearts that I've seen before include "See 23" , "They beat" , "quarterdeck?" , "Card suit and essential organs" , "Scots club nickname; suit" .)

I've seen this clue in the Irish Times (Crosaire) and the Irish Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.