3 sentences

1. 我下狠心一定要把这笔生意谈成。

   wǒ xià hěn​xīn yī​dìng yào bǎ zhè bǐ shēng​yi tán chéng.

   I've made up my mind to close this deal at any cost.

   Source: Dong Chinese Dictionary

2. 他狠了狠心，卖掉了陪伴自己多年的老车。

   tā hěn le hěn​xīn, mài​diào le péi​bàn zì​jǐ duō nián de lǎo chē.

   He steeled himself and sold the old car that had been with him for many years.

   Source: Dong Chinese Dictionary

3. 他竟然这么狠心，丢下生病的妻子不管。

   tā jìng​rán zhè​me hěn​xīn, diū​xià shēng​bìng de qī​zi bù​guǎn.

   He was so heartless that he left his sick wife unattended.

   Source: Dong Chinese Dictionary