Heida sings on song # 13 of the album: "Efter 100 Ár".
On Song # 7 "Heimsk Ást", Heida is co-writer.
I found A Review of the Album online (2004):
Dr. Gunni's album Stóri Hvellur? Well, I can say that while some things have changed for the better, such as the album being sung in Icelandic, some things have thankfully NOT changed. Stóri Hvellur is a very solid Pixies/Rocket From The Crypt sounding chunk of rock sugar, though weirder and noisier in moments. Gunni seems to have assembled himself an amazing tight backing rock band, especially given how distorted and rough his solo bedroom demos available for download on his site sound. (See? Didn't I tell you Gunni has the best web site in the world?) Whereas, IMHO, I can count the number of Weezer hooks I've heard over the span of their four albums on two hands, Dr. Gunni nails 15 hooks on this single 15 song album, one after the other. The songs sound heavier and fuzzier than they did with Bless, and, at times, more poppy than anything Gunni has written before.. but Gunni vocally still very much sounds like Gunni, and he's more upfront in the mix than ever before, which is what makes this record stand out amongst all the other Pixies, Weezer, or Rocket influenced bands. His voice is easily the strangest thing about the music, but, wow, if that voice doesn't have the greatest personality -- no matter if you can understand Icelandic or not. No one can belt out a yell or yodel quite like Gunni can.. and this can either be an acquired taste, or a permanent bad taste (no pun intended!). If you have any inkling of a sense of humor, you'll appreciate the voice, and the tight, sonic production on this record, and how amazingly colorful, vibrant, and fun every song on the record sounds. I can't list song highlights, because every song is a winner - although my current favorites are "Alltaf Meir", "Heimsk Ást", "Eftir 100 Ár", and the three-part rock opus "Undo (Pabbi Þinn/Ctr-Alt-Esc/Mamma Þin)" which actually clocks in at over *gasp* five minutes!
Even though it was released last year, Stóri Hvellur is so amazing, I'm going to cheat and adopt this as a 2004 release and claim this is as my favorite record of the year so far.