* Home Depot raises outlook, shares jump
* Carnival guides lower once more, shares tumble
* JPMorgan shareholders to decide on Dimon's chairmanship
* Futures: Dow up 11 pts, S&P, Nasdaq flat
By Rodrigo Campos
NEW YORK, May 21 (Reuters) - U.S. stock index futures were little changed on Tuesday after the S&P 500 hit yet another intraday record in the previous session, with markets expected to drift sideways ahead of Congressional testimony from Fed chairman Ben Bernanke on Wednesday.
The U.S. economic calendar is thin and the market will continue to be vulnerable after the S&P and Dow industrials hit record highs on Monday. However, the expectation of continuing accommodative monetary policy from the Federal Reserve should continue to lend support to equities.
"Given there's not a lot of economic news coming out today, it looks like we're set up for a pretty 'nothing' day," said Kim Forrest, senior equity research analyst at Fort Pitt Capital Group in Pittsburgh.
She said company-specific news will be the focus and the market is "nervous" ahead of Bernanke's testimony, "but not enough to take any action, apparently."
The housing market recovery helped Home Depot report higher quarterly sales and earnings, prompting the world's largest home improvement chain to boost its sales outlook for the year. Its shares rose 3.6 percent in premarket trading.
S&P 500 futures were flat and little changed in terms of fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures rose 11 points, and Nasdaq 100 futures were unchanged.
Carnival Corporation & Plc slashed its full-year earnings outlook for the second time in less than three months as it expects lower revenue due to the lower ticket pricing it is employing to attract passengers following a string of high-profile mishaps. Its U.S. shares dropped 7 percent in premarket trading.
Best Buy shares fell 1.8 percent in premarket trading after the world's largest consumer electronics chain reported weaker-than-expected quarterly sales and warned that investments to win back shoppers could squeeze profits in the near term.
Shares of JPMorgan Chase & Co were flat in premarket trading as final ballots come in on a proposal to strip the bank's chairman and chief executive Jamie Dimon of his chairman title. Investors worry about what will happen if shareholders win what will likely be a close vote.
Apple chief executive Tim Cook is expected to testify before Congress later on Tuesday after a U.S. Senate report on the company's offshore tax structure said the iPhone maker has kept billions of dollars in profits in Irish subsidiaries to pay little or no taxes to any government. Apple shares fell 0.8 percent in premarket trading.
Medical device maker Medtronic Inc reported a better-than-expected quarterly profit driven by strong international sales and its shares rose 5 percent in premarket trading.