River's in the heart of Sweden, I learned (4)
I believe the answer is:
nile
'river's' is the definition.
(Nile River is an example)
'heart of sweden i learned' is the wordplay.
'heart of' indicates a hidden word.
'NILE' can be found hidden inside 'sweden i learned'.
'in the' is the link.
(Other definitions for nile that I've seen before include "long-distance runner in Africa" , "World's longest river" , "Egypt's river" , "Cleopatra's river" , "River that's Blue and White" .)