1. What does it mean?
심쿵 compresses the image of 심장이 쿵, a heart going thump. It describes a flutter of excitement in response to an appealing person, a touching gesture, or something irresistibly cute.
Also written or said as 심쿵하다, heart flutter
2. The nuance
The feeling does not have to be romantic. A pet greeting its owner can prompt the same caption. This is figurative language about a reaction, not a medical description; in ordinary use 심쿵하다 means to have that fluttering moment.
3. Examples
“친구가 내 취향을 기억하고 선물을 골라서 심쿵했어.”
My friend remembered my taste and picked a gift for me. My heart melted.
“강아지가 내 발에 기대 잠드는 모습에 심쿵했어.”
Seeing the puppy fall asleep against my foot made my heart flutter.
Sources
KoreanClass101: Korean language lessons
References support the meaning and usage. Example sentences are written for NoCapWiki.