Swimming helps to keep her heart and lungs healthy and it is a good way to keep fit.

　　Swimming helps to keep her heart and lungs healthy and it is a good way to keep fit.
　　游泳能使她的心脏和肺健康,这是一个很好的方式来保持健康.
动名词Swimming 作主语
　　动名词已经将动作名词化了,它不再强调动作本身了,它已把某个动作视为某种活动或是某件事情了.比如说,动名词常在句中作主语、直接宾语；我们都知道,在句中作主语、直接宾语的词只有是名词、代词,因此从某种意义上说,动名词就相当于名词、代词了.
例如：
Climbing up the mountain will make you exhausted.
爬上这座山会使你筋疲力尽.
Stop talking please.请不要讲话.