[dleviwing]

There is Inertial mass, Gravitational mass, and Relative mass. Heavy is a reference to weight and thus is not mass but is a reference to the effect of gravity on a body; a very common error of the science novice.

To answer your question, you need to know what gravity really is. Any good thoughts on the topic?
To me, gravity is the process of condensing spatial matter into particle matter structures or the conversion of long wavelength states to short wavelength states.