雄心(xióngxīn), ‘the ambition’ in English, means positive pursuit and noble dream and can match with 壮志(zhuàngzhì) ‘great dream’. For example,
I appreciate his ambition.
野心(yěxīn), express a negative meaning when describing someone. As the morpheme 野(yě) originally means ‘suburb’ and extended its meaning into ‘out of rule’ and implies ‘injustice’, 野心(yěxīn) means ‘ruthless ambition’ and is used to describe the person who wants to gain things that don’t belongs to him. For example,
He only hopes to do the current works well and doesn’t have the ambition like others.