心狠的英文：
cruel; merciless

参考例句：

Heart is cruel and disposition ruthless
心狠性悍

He is evil-minded. (The man is cruel and evil.)
他的心很黑。(这个人手狠、心狠)

In this business you have to be tough,and the devil takes the hindmost.
干这一行必须心狠，谁顾别人谁吃亏。

cruel是什么意思：
adj. 残忍的；残酷的；令人极痛苦的；刻毒伤人的；惨痛的

Cowards are cruel
懦夫不仁

How can fate be this cruel?
命运为何如此残酷?

This is a cruel joke at my expense.
以我为代价的残酷笑话。

It hurt me something cruel.
弄得我痛极了。

He was cruel, treacherous and unscrupulous.
他残忍、奸诈、不择手段。

merciless是什么意思：
a. 无慈悲心的,残忍的

The indigenous people were merciless towards the immigrants.
当地的土著对外来移民可谓赶尽杀绝。

There is not on earth a more merciless exactor of love from others than a thoroughly selfish woman.
一个自私透顶的女人，在榨取爱情时比谁都厉害。

North Korea has warned it will take what it calls
朝鲜方面发出警告称，如果美国及其盟国依旧试图在公海拦截他们认为是可疑的朝鲜船只，朝鲜将会进行“残忍的报复行动”。

The ruthless methods used in the past -- the over-simplified, one-sided, crude, excessive criticism and merciless attacks -- must never be repeated.
过去那种简单片面、粗暴过火的所谓批判，以及残酷斗争、无情打击的处理方法，决不能重复。