If you are going to undergo a Liver Flush I would attempt it before a water-only-fast.
Personally I would not undergo a Liver Flush as I do not see the need for one personally as the fast (if conducted properly) will cleanse the entire body and especially so if proper living habits are adhered to post fast.
The Liver is one of the Major organs of elimination but once the bulk of toxins have been eliminated the bodily organs will also self cleanse via autolysis.
At the age of 57 I still have a resting pulse of 60 and a blood pressure that varies between 120/80 or slightly below that.
At the end of a long fast when the major organs have been cleansed, the beating of the heart is as clear and as smooth as a bell. There is nothing quite like it except when you compare it with that of a child's beating heart.