With its once high-flying spine and cardiac-rhythm businesses struggling, Medtronic Inc. forked over more than $1 billion Monday to buy what it believes will be the next big hit in medical technology -- devices used in minimally invasive surgery to replace faltering heart valves.

The Fridley-based company is buying CoreValve Inc., Irvine, Calif., for at least $700 million, and Ventor Technologies Ltd. of Israel for $325 million. Both are developing new ways to replace heart valves in patients.

Medtronic said the CoreValve treatment could initially serve as an alternative for about 300,000 people worldwide who are high-risk patients in poor health and can't tolerate open-heart surgery.

"Surgery to replace aortic valves is very successful; patients who have their valves replaced do quite well,'' said Scott Ward, president of Medtronic's CardioVascular division. "But there are patients now who are not surgical candidates.''

Operations to replace poorly functioning heart valves are common but require open-heart surgery that involves cracking open the patient's chest, resulting in a long recovery. Surgeons use a mechanical valve or one crafted from human tissue or harvested from an animal, such as a cow or pig.

The U.S. market for heart valves is about $650 million, according to Frost & Sullivan. "It's pretty standard fare in medical technology [that] once a midsized company reaches a certain size it gets acquired,'' said Venkat Rajan, an analyst with the market research firm. "In this case, if Medtronic didn't buy these companies, somebody else would have."

While the market for tissue valves is growing steadily but not spectacularly, demand for mechanical valves has waned.

Enter CoreValve's ReValving System technology -- now available only outside the United States. The tissue valve is inserted into the heart on a catheter through the femoral artery in the groin, much like a cardiac stent.

Ward said that as clinical evidence supporting the technology is gathered and as doctors become comfortable with the technique "you'll see a greater and greater level of adoption, especially as patients demand access to less-invasive approaches."

CoreValve's system received European regulatory approval in 2007, and competes against a similar device made by California-based Edwards Lifesciences. Ventor Technologies is conducting clinical trials of a minimally invasive surgical procedure that involves inserting the valve through a small incision in the chest.

Medtronic hopes to launch the Ventor device outside the United States in 2011, with U.S. launches expected for both companies' products expected in 2014.

Richard Bianco, director of the Experimental Surgical Services department at the University of Minnesota, is skeptical about the existing technology, saying more clinical tests are needed to prove it works long-term and is safe.

But he added, "I'm supportive of Medtronic getting involved, because the company has high ethical standards and will conduct clinical trials in the right way."

Timothy Nelson, an analyst at FAF Advisors in Minneapolis, said new heart valve technologies "are clearly the most exciting thing on the horizon in medical technology."

Even so, Nelson said getting Food and Drug Administration (FDA) approval for the technology will be time-consuming, expensive and not necessarily automatic.

"We need to see good data first," he said.

Medtronic's acquisitions come at a time when the company has seen sales slow in its biggest business -- pacemakers and heart defibrillators -- following the 2007 recall of a defibrillator wire. In addition, revenue in its spine division has been sluggish after the FDA issued a safety warning last summer about a bioengineered product used in spine fusion surgery.

Beyond developing new technologies internally, Medtronic has historically grown its business by making key acquisitions.

"Medtronic is very committed to growth,'' said Medtronic's CardioVascular division's Ward. "We're a growth company that has been in the valve business for 30 years. These two companies position us for a leadership position for many years to come."

Medtronic's stock closed Monday at $34.02, up 2 cents.

Janet Moore • 612-673-7752