idiom · ungrateful, cruel, or lacking a conscience; unfeeling toward others

他是个没心没肺的人，完全不顾及家人的感受。

expression · thoughtless, mindless, or extremely forgetful; lacking attention to detail

我这人没心没肺的，刚才还拿着钥匙，转眼就找不到了。

expression · guileless, innocent, or carefree; having a disposition that does not harbor worries or complex schemes

她整天没心没肺地傻笑，好像从来没有烦恼。