Padilla, who lost by two votes, has requested a recount. Nearly 38,000 ballots were turned in.
"That's well within margin of technical error and it's important to review those ballots very carefully to be sure every vote was counted," Padilla said.
The recount is scheduled to begin Wednesday morning and is expected to last a couple of days.
Initially, only 25 of the 110 precincts in Chula Vista will be counted.
If miscounts are detected in this sample size, all of the votes will be recounted if Padilla requests it.
Michael Vu of the San Diego County Registrar of Voters said Padilla and the Democratic Party are paying $12,000 a day for the recount.
Meanwhile McCann, who has been declared the winner and has been sworn in, said he's not worried about the recount.
"We've never trailed so we believe that during recount we're going to be good and if they feel there's a statistical possibility, that we will probably gain votes," McCann said.