* Pfizer, Merck rise as results beat expectations
* Herbalife shares tumble after it cuts sales outlook
* Futures up: Dow 33 pts, S&P 3 pts, Nasdaq 7 pts
NEW YORK, July 29 U.S. stock index futures edged higher on Tuesday following better-than-expected results from companies such as Pfizer and Merck and ahead of data on home prices and consumer sentiment.
* Merck reported better-than-expected quarterly results as new drugs offset declining sales of ones facing generic competition. Pfizer's higher-than-expected second-quarter earnings were helped by growing sales of its cancer medicines.
* The economic calendar for Tuesday includes S&P/Case-Shiller home price index for May at 9:00 a.m. EDT (1300 GMT) and the Conference Board's consumer sentiment for July an hour later.
* Later on Tuesday, the Federal Reserve begins a two-day meeting on monetary policy. The Fed could make subtle yet telling changes to its policy statement due Wednesday, as it plans how and when to eventually raise interest rates.
* S&P 500 e-mini futures were up 3 points and fair value - a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract - indicated a slightly higher open. Dow Jones industrial average e-mini futures rose 33 points and Nasdaq 100 e-mini futures added 7 points.
* Shares of health insurer Aetna rose after it reported a higher second-quarter profit, helped by last year's acquisition of Medicare and Medicaid provider Coventry Health Care.
* Spirit Airlines rose 2.6 percent in light premarket trading after the low-cost U.S. carrier reported a 54 percent rise in second-quarter profit.
* Costco shares rose 2.2 percent premarket after Goldman Sachs added the stock to its conviction buy list.
* Herbalife cut its sales outlook for the year after raising it three months earlier, following billionaire investor Bill Ackman's latest round of accusations against the company last week. Shares of the weight-loss and nutrition products company slid 11.4 percent in premarket trading. (Reporting by Rodrigo Campos; Editing by Bernadette Baum)