Small pig hearts tough to pierce with a blade (3,7)
I believe the answer is:
run through
'pierce with a blade' is the definition.
(run through can mean to pierce with a blade)
'small pig hearts tough' is the wordplay.
'small pig' becomes 'runt' (as in the runt of the litter).
'hearts' becomes 'h' (abbreviation used in card games e.g. bridge).
'tough' becomes 'rough' (synonyms).
'runt'+'h'+'rough'='RUN-THROUGH'
'to' is the link.
(Other definitions for run through that I've seen before include "Have a stab at" , "Rehearse" , "To transfix with sword" , "blow" , "Rehearsal" .)