悸
[jì]
'Fluttering/Pounding', refers to the state where the heart beats heavily, normally triggered by various strong stimuli like love, fear, anticipation and so forth, conveying that at this moment, one may be excited, surprised or nervous because of certain reasons, generally associated with intense psychological activities or sudden occurrences. This word is quite simple yet profound enough to imply lots of possibilities without being explicitly defined, evoking reader’s personal interpretation accordingly.