I can't find anything either. Also, the spelling of the name is rather strange. Considering the inlay of the male deer head on the headstock, I wonder if they meant for the name to be Hart Man, but misspelled it as Heart Man 
 
 
"Hart
Pronunciation: \ˈhärt\
Function: noun 
Etymology: Middle English hert, from Old English heort; akin to Latin cervus hart, Greek keras horn — more at horn
Date: before 12th century
chiefly British : the male of the red deer especially when over five years old : stag"