While this looks a good deal like a model from the Kirsten Pipe Company at first glance, Sweetheart is indeed a separate brand. This one is appears to be an earlier "Sweetheart", with the stamping on the top face of the shank in script and a heart shape next to that, then in block letters "MADE IN U.S.A.".
The shank is a fluted hexagonal cross section and the internal filtering device permits ingress of air from the front of the pipe on drawing on the pipe.
A patent was filed in 1958 and was issued on Aug 7 1962 to a Philip J Stieger of St.Paul Minnesota... US Patent #3,048,179. This version may vary quite a bit from the actual production pipe.
Source information courtesy SmokingMetal.co.uk