They're back.

Boston Scientific Corp., one of the nation's biggest medical device firms, said Thursday that it has won clearance from U.S. regulators to resume shipments of two popular models of heart defibrillators -- after recalling its entire portfolio of the lucrative devices a little over a month ago.

The decision, issued by the Food and Drug Administration (FDA), comes after a 30-day review conducted by the federal agency. Natick, Mass.-based Boston Scientific, which employs about 4,000 in the Twin Cities, had asked regulators to approve changes in the manufacturing process for defibrillators on March 15 and 16. The FDA mandates that medical device companies inform the agency of such changes. Boston Scientific's Arden Hills-based Guidant division, which makes the devices, employs about 2,000 in the Twin Cities.

Tim Nelson, an analyst with FAF Advisors, said "this happened much faster than I expected. I never thought the FDA would move this quickly."

The company said Thursday that two models of devices -- the Cognis cardiac resynchronization therapy defibrillator (CRT-D) and the Teligin implantable cardioverter defibrillator (ICD) -- will be available to U.S. customers immediately. The two devices represent "virtually all" its defibrillator implants in the United States, the company said.

Defibrillators are $30,000 stopwatch-sized implantable devices that shock an errantly beating heart back into rhythm.

Initially, the company recalled seven models of the devices.

On Thursday, Boston Scientific said an internal review found a "few additional instances" where manufacturing changes to the Confient, Livian, Prizm, Renewal and Vitality models were not submitted. The company said it is "working closely" with the FDA to secure clearances to market those devices, as well.

Boston Scientific CEO Ray Elliott said in a statement that the company is "committed to doing the right thing every time, and we acted voluntarily, swiftly and appropriately to ensure compliance with all regulatory requirements. Our entire sales force is energized and hard at work!"

Speculation has been rampant among investors and Wall Street analysts about how much market share Boston Scientific has lost to its rivals in the defibrillator market -- Fridley-based Medtronic Inc. and St. Jude Medical Inc. of Little Canada.

According to an April 12 note to investors issued by Wells Fargo Securities analyst Larry Biegelsen, the recall will lower Boston Scientific's 29 percent share of the $4.3 billion U.S. market for ICDs by 5 percentage points. Before the recall, Boston Scientific was No. 2 in the ICD market, behind market leader Medtronic.

The extent of the financial damage may be divulged April 26 when the company reports first-quarter earnings. Boston Scientific shares rose 7 percent late Thursday in after-hours trading to $7.65 after closing at $7.14, down 2 cents, in New York Stock Exchange trading.

Bloomberg News contributed to this report. Janet Moore • 612-673-7752