Jacob, apologies I was rushing and should have typed centre not heart free. Yes the product is cut to size at the mill removing the centre (pith) and then kiln dried. As opposed to the old days where we convert 100x200mm or 100x225mm.
Chances are they're referring to Southern Yellow Pine, could even be referring to Oregon Pine or Columbian Pine which in essence I Douglas Fir. All widely available in the UK in clear grades from specialist timber importers.
For a more rustic look (not sure who brings it in these days) but you...
Johnny Accoya is derived from plantation grown Radiata Pine (New Zealand and South America hence the wide growth rings compared to Redwood) and grows in a fraction of the time which gives the clear sections and long lengths. Now compare that to a Pine tree growing in a far colder climate to...