My 2000 LaSabre is always heating to the midway mark on the gauge, why? I turn on the heater but its summer?

Depending on the car, the makers started leaving the numbers off the gage and only put "C" and "H" on each end of the gage. In this case, normal operating range is in the middle. If the car is loosing water, or other things that lead you to believe it is running too hot, take it to someone you trust and have it checked. For under $20 you can now buy digital thermometers that you point and shoot...you can aim them at different parts of the engine and get an accurate temp reading...they are also handy in the home for checking the furnace output and even food tempature.