with hearts a-thump

[frindle]

Hello. I'm not sure what 'with hearts a-thump' means in the context.
Does it mean the boy's heart doesnt beat fast now?
Please help! Thank you.

Now what? Now what do boys
so clever, brave and true,
with hearts a-thump for bears so fine
and Mamas sleeping in the night...
what do they do?


(In the picturebook, the boy made a big bear rumble into the hole he had made. And at first, he shivered and his heart kept thumping!
But now, finally the bear is asleep, he isn't afraid of it anymore.)

[Ouisch]

A thumping heart is one that is beating very hard, so much that you can feel it in your chest and you feel as if you can hear it beating. Very strong emotions can cause a heart to thump - fear, excitement, anticipation, etc.

[frindle]

Thank you^^