一心一意----with undivided attention

例句:
A: He,s really attentive to his work.
他做事的确用心。
B: Actually，he often works with undivided attention.
事实上，他经常是一心一意地做事。

同义词:heart and soul; heart and hand

注释:be attentive to 留心···，注意···
with attention 留心地；注意地