Several letter clusters require you to breathe out (exhale) a little bit before the letters. This tiny “h”-sound appears before kk, tt, and pp along with a few other letter clusters.
Pronouncing it takes practice. When pronouncing a word such as “ekki” ([e(h)ki]), you first say the “e” sound, then you stop using your voice and you breathe out a little bit, and then you say the “k”. If you place your hand in front of your mouth, you should feel the wind on your hand. You should not constrict your throat, this is just a normal h sound like in “hand” but not a throaty h sound like in “Bach”.
This short breath is extremely important, without it people are unable to understand what you’re trying to say. “Ekki” (“not”) without the exhalation is “eggi” (“of an egg”), “bakka” (“drive backwards”) without the exhalation is “bagga” (“to use mouth tobacco”), and “vakna” (“to awaken”) without the exhalation is “vagna” (“of wagons”). For that reason, it is far better to exaggerate this sound significantly rather than not doing it enough.

Double letters

The tiny exhalation always appears before the letters kk, tt, and pp:
  • kk
    • ekki ([e(h)ki]), dekk ([de(h)k]), bakka ([ba(h)ka])
  • tt
    • köttur ([(h)tur]), létt ([(h)t])
  • pp
    • hoppa ([ho(h)pa])

Others

It also appears in the following letter clusters:
  • kn
    • vakna ([va(h)kna]), undantekning ([undante(h)kning]), reknir ([re(h)knir])
  • kl
    • jöklar ([(h)klar]), sjúklingur ([sjú(h)klingur]), Hekla ([he(h)kla])
  • tn
    • vatn ([va(h)tn]), setning ([se(h)tning])
  • tl
    • vitlaust ([vi(h)tlaust]), litli ([li(h)tli])
  • pn
    • opna ([o(h)pna])
  • pl
    • epli ([e(h)pli])

Effects of stress

The small exhalation is only necessary when the syllable has stress (emphasis). If the word doesn’t have stress, you can omit the breath. You can see the difference in:
  • það er EKKi RÉTT” (meaning “that’s not true”) is pronounced [það er e(h)ki rétt]
  • ÞAÐ er ekki RÉTT” (meaning “that's not true”) is pronounced [það er iggi rétt].