3 sentences

1. 她整天没心没肺地傻笑，好像从来没有烦恼。

   tā zhěng​tiān méi​xīn​méi​fèi de shǎ​xiào, hǎo​xiàng cóng​lái méi​yǒu fán​nǎo.

   She giggles lightheartedly all day, as if she doesn't have a care in the world.

   Source: Dong Chinese Dictionary

2. 他是个没心没肺的人，完全不顾及家人的感受。

   tā shì gè méi​xīn​méi​fèi de rén, wán​quán bù gù​jí jiā​rén de gǎn​shòu.

   He is a heartless person who completely disregards his family's feelings.

   Source: Dong Chinese Dictionary

3. 我这人没心没肺的，刚才还拿着钥匙，转眼就找不到了。

   wǒ zhè rén méi​xīn​méi​fèi de, gāng​cái hái ná zhe yào​shi, zhuǎn​yǎn jiù zhǎo bù dào le.

   I'm so scatterbrained; I was holding my keys just a moment ago and now I can't find them.

   Source: Dong Chinese Dictionary