I built a icf house last year this is the first winter we will be living in it we installed infloor heat in the garage floor now when we use the in floor heat to melt the snow off the cars we notice that there is abunch of moisture in the air in the garage how do we get rid of the moisture

You need to vent the moist air back outside. A ventilator with a humidity control, or a timer triggered to run for a set ammount of time after the garage door is operated would probably take care of the issue. How long it takes the vehicle to dry/all the moisture to evaporate will determine when and how long a timed ventilator would need to run. And of course anything you can do to get the bulk of the water to drain away quickly before it evaporates will really help, but a good slope and drain would have had to be put in place before the slab was poured.

If you don't have a good drain, you could probably add a rubber drain pan with a pump or vacume collection device to process more water before it gets converted to vapor by the warm floor...

garage floor drains are at best a bad idea, if not illegal, unless you have a set up where you can process waste petroleum. a good automatic fan with a timer is the best bet.