Matthew 12:40 For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.
prolonged from a primary kar (Latin cor, "heart"); the heart, i.e. (figuratively) the thoughts or feelings (mind); also (by analogy) the middle:--(+ broken-)heart(-ed).
Unless I'm mistaken, the heart, in relation to our chests, it resides in the middle. In the Matthew 12:40 passage, it is the earth where Jesus would spend three days and three nights in the middle of. Since the earth would be like this huge round ball, where then would the middle be found? 6 foot below the earth? A tomb above the earth? Or actually in the middle of the earth somewhere?
But as Percho has already pointed out, there were two compartments there at the time, with a great gulf fixed between the two. Logically then, Jesus went to the good compartment during that time, setting the captives free, meaning those in Abraham's bosom. Afterall, until someone could defeat death and get the keys to death, no way for them to rise to immortality, or anybody for that matter. Jesus had to defeat death so that we could as well.
But those who conclude Jesus went to heaven to be with the Father those 3 days and 3 nights, well that's not what Scripture says.