The difference between 费心 and 用心
These verbs are similar in meaning, but they are used in different situations.
The verb 费心
The verb 费心 
emphasizes that a person spends a lot of time thinking about a question or doing something.
emphasizes that a person spends a lot of time thinking about a question or doing something. Pay attention
It is usually a troublesome action.
Examples
为妈妈准备礼物要费心一些
Making a present for mom is a bit of a hassle
wèi māma zhǔnbèi lǐwù yào fèixīn yìxiē
很多人如今不费心举办婚礼了
Nowadays many people do not bother to organize their wedding
hěn duō rén rújīn bú fèixīn jǔbàn hūnlǐ le
他在抨击那部电影前并没有费心去看看电影
He didn’t bother to see the film before criticizing it
tā zài pēngjī nà bù diànyǐng qián bìng méiyǒu fèixīn qù kànkàn diànyǐng
The verb 用心
The verb 用心 emphasizes that a person invests a lot of energy and emotional into something.
emphasizes that a person invests a lot of energy and emotional into something.
Examples
女人希望男性能够用心听听她们的心声
Women want men to listen to their hearts attentively
nǚrén xīwàng nánxìng nénggòu yòngxīn tīngtīng tāmen de xīnshēng
她用心念书了
She studied hard
tā yòngxīn niànshū le
在我成长的过程中，我记得有人用心教导我
I remember that when I was growing up, someone put their heart into teaching me
zài wǒ chéngzhǎng de guòchéng zhōng, wǒ jìde yǒurén yòngxīn jiàodǎo wǒ
用心 as a noun
用心 also can be a noun meaning "hidden intention".
Pay attention
This verb is often used in the set expression 别有用心 .
.Examples
她怀疑他想再见她一面是别有用心
She suspects that he has ulterior motives in wanting to see her again
tā huáiyí tā xiǎng zài jiàn tā yí miàn shì bié yǒu yòngxīn
她对我这么好，一定别有用心
She’s so nice to me. She must have a hidden agenda
tā duì wǒ zhème hǎo, yídìng bié yǒu yòngxīn