Everithing works only the heater not work

ALWAYS UNPLUG YOUR DRYER BEFORE ATTEMPTING TO DO ANY WORK ON IT.
Sounds like your problem may be with the heating coil.
Remove the back of the machine and try to locate the air duct going from the blower to the drum. Normally inside the air duct you will find the heating coil and the thermostats/thermistor.
Once you have located the heating coil, remove the two wires from it and check the coil with an ohm meter across the two terminals of the coil.
You should read continuity across the terminals, if not you will need to replace the coil as it is faulty.
If the heating coil is ok, then:
You can check the thermostat/thermistor by removing the two wires and taping them together with electrical tape.
If the coil heats up then replace the thermostat/thermistor.
DO NOT LEAVE THE WIRES TAPED TOGETHER AFTER THE TEST. This could cause a fire, as you have removed the saftey of overheat from the machine.
I will include these two websites for parts and further help:
http://www.partselect.com/
http://www.appliancepartspros.com/index.aspx
Both also have chat assistance 24/7.
Good Luck,
Hope this helps