Compression on 2000 monte carlo

What is the compression supposed to be on a 2000 monte carlo 3.4 It is running hot and the heater is not working

You won't find a "spec" for compression numbers. After checking compression on all cylinders, the lowest number should be within 30% of the highest number.

Have you checked for coolant leaks? Sure you don't have a lower intake gasket leak?

How do I check the intake gasket When it gets hot the heat light will come on; you can turn it off and wait a few minutes then the heat hand will drop back down to around 160 or 170 but the heater want heat; and the car want get hot again; you can let it set and idle and the fans will come on and the heater will work good but when you start driving it the heater stops heating and goes cold; the compression on the heads are running from 90 to 125

Could be air bound, bleed the system first. BTW 90 is low for that engine at normal cranking speed, throttle held open.