Hi if it has low compression then this will mean one of three things the first and most likely is that the head gasket has gone this can be replaced but your head will need sending off to be pressure tested and skimmed to make sure it will work when refitted.
the second problem could be a cracked head in this case the head and gasket will need replacing but remember to check the thermostat and water pump as this can cause the head gasket to blow and could be the cause of the problem in the first place so get these parts checked

the third problem could be blown piston rings this is less likely unless the car has been driven with no oil.

let me know if you need further assistance ok