In the transition of Persian from Old Persian to Middle Persian and finally to New Persian, there is a significant phonemic change: reduction of VCV to either of the V's (V: Vowel, C: Consonant). During this process, the phoneme sequence Vowel-Consonant-Vowel is reduced to one of the vowels and consequently, the consonant and the other vowel disappear:

Avestan /
Old Persian
Middle Persian New Persian
shiyâti shâti shâdi
chavant chant chand
duvar dar dar
khshâyathiya shâha >> shâh shâh

New Persian Dialects

New Persian per se, is more than 1100 years old and naturally, VCV phoneme reduction has occurred in the modern forms of Persian as well. There are many reductions both in the standard dialect and regional dialects. Interestingly, in some dialects, a different V has left the language, resulting in having, for example, both "minam" and "monam" as the reduced forms of "mikonam".

Full Form Reduced Form
pirâhan piran
nevardebâm nardebâm
khwâhar khwâr
barâdar barâr
khâsiye[1] khâye
khodemun khomun

[1] VCV rule can help us in retrieving the older form of words. I found "khâsiye" in a book about Persian dialects in Shahr-e Bâbak. "khâsiye" reveals the older form of the word "khâye" (testicle).

Reduction in Conjugation

VCV reduction is extensively found in the conjugation of verbs in spoken Persian:

Full Form Reduced Form
mishavam misham
miravam miram
mikhwâham mikhwâm
midaham midam
mitavânam mitânam >> mitunam
miguyam migam, migum
miyâvaram miyâram
migozâram mizâram
mikonam minam, monam
mibinam minam
midânam minam
rafte budam raftudam