Wal-Mart (WMT) shares added more than 2% at the start of the week after an upgrade from Citigroup.

Citi, which raised its rating to buy from hold and its price target to $65 from $54, said the move comes as Wal-Mart has improved the customer experience, prepared to capitalize on apparel and become more aggressive on prices.

We have stayed on the sidelines with the food retailers even with food inflation on the horizon in anticipation of WalMart getting more aggressive on price, wrote Deborah Weinswig, adding that it s finally happened.

Negative traffic comparisons in the last quarter of 2009 showed that WalMart might be losing customers it gained during the recession, says Weinswig. The savings are no longer enough to keep customers from returning to their supermarkets, and thus as the economy improves, the analysts says the retailer is likely to significantly increase rollbacks.

The bottom line: WalMart is lacing up the gloves in the fight to win the modern day price war in food retail in 2010, Weinswig wrote.

Boston Scientific Down

Boston Scientific (BSX) shares fell sharply Monday after the company put a halt on defibrillators devices that detect rapid and irregular heartbeat and shock the heart to restore the normal rhythm.

The company said it stopped shipment and is retrieving all field inventory for its implantable cardioverter defibrillators and cardiac resynchronization therapy defibrillators because it discovered two instances of changes in its manufacturing process that weren t submitted to the FDA.

The changes, which affect eight of Boston Scientific s product families, don t introduce any risk to patient safety that the company knows of, according to a press release.

The bottom line: Boston Scientific said it will provide an update on the financial implications after an evaluation. Given the financial uncertainty involved, these actions could have a material impact on the Company's previously issued guidance, including revenue, operating profit and cash flows for the first quarter and full year of 2010, according to the release.