Bob Hatzenbeller walked out of a Minneapolis hospital on Monday with a new mitral valve in his heart and no massive scar on his chest.

It was a landmark occasion, at least for diseases of the mitral valve. Hatzenbeller became the first human patient in the United States to have a mitral valve implanted deep in his heart using a pioneering technique that didn't require doctors to stop his heart during the operation.

Hatzenbeller's titanium-and-nickel bioprosthetic heart device was made by Roseville-based Tendyne Holdings Inc., one of several companies striving to create a multibillion-dollar market in minimally invasive mitral valve replacement. Last week the company got approval to start a 30-patient global study to see if the devices are safe.

Doctors praised the decision by the Food and Drug Administration to let very early-stage human implants of Tendyne's device move forward, because similar devices have been held back for years while other countries used them first. "It signals a shift in the regulatory perspective," said Dr. Paul Sorajja, cardiologist and researcher on Hatzenbeller's care team at Abbott Northwestern Hospital. "Here we're basically at the same level as the rest of the world with these valves."

Valves control the pace of blood through the heart, and they become lethal when diseased. But having traditional surgery to replace heart valves can be a traumatic experience, especially for older and more complex patients who have a difficult time recovering from a large chest incision and the unpredictable effects of unusual blood flow. Engineers and physicians have been developing ways to deliver new valves to diseased hearts on the ends of long tubes called catheters that can be snaked through the body without big incisions.

The aortic valve was the first one for which companies developed a "transcatheter" replacement therapy. More than 150,000 have been done worldwide, mainly in patients who are too sick for traditional heart surgery. As the procedure becomes more common, doctors expect less-risky patients to start getting it and worldwide revenue will eventually climb past $3 billion a year.

But treating diseased mitral valves like Hatzenbeller's through transcatheter procedures is a new frontier in valve surgery. Roughly three dozen people worldwide have had one of the several experimental mitral replacement valves implanted.

Hatzenbeller, 76, of Cumberland, Wis., became the first in the U.S. last week, at the Minneapolis Heart Institute at Abbott Northwestern Hospital. He declined to do media interviews just after being released from the hospital.

Physicians and stock analysts generally agree that the mitral-valve market is three to four times the size of the aortic one, based on incidence of disease.

It's not clear what the mitral valves would cost, since they're only available in the U.S. under investigational device exemptions from the FDA. Dan Mans, an executive with Tendyne, confirmed the company expects to charge a price "at or above" the going rate for aortic valves, which is roughly $30,000 today, though the price has not been officially set.

Last week, the FDA granted Tendyne an investigational device exemption that will let the company pursue cutting-edge human research on patients that have a condition called mitral regurgitation.

That's the condition in which the mitral valve lets some of the blood flow backward in the heart, reducing its effectiveness. About 3.5 million people in the United States, and double that figure globally, have regurgitation. Severe forms of the condition have a 50 percent mortality rate at five years, according to clinical research cited by Tendyne.

Numerous companies are pursuing minimally invasive valve therapies for mitral regurgitation, including several with ongoing studies. Some are looking at whether aortic valves can be used in the mitral position, while others are developing ways to repair rather than replace the valve. Some, like Tendyne, are developing valves specifically for the mitral replacement.

A spokeswoman for Medtronic PLC, which has its operational headquarters in Fridley, confirmed the company is developing mitral repair and replacement technology, as well as monitoring new developments for future investments.

Last month, analysts with Leerink Partners said a Canadian company called Neovasc appeared to be the market leader for transcatheter mitral replacement valves because it had implanted six international patients. Another small company based in Massachusetts, CardiAQ Valve Technologies, got FDA approval for an investigational study last week, just like Tendybe did.

Doctors at the Minneapolis Heart Institute Foundation, the not-for-profit research group at Abbott Northwestern doing the research, praised the FDA for allowing early-stage human implants of mitral valve replacements. They said the agency may have been influenced by the relatively slow adoption of transcatheter aortic valves.

"Patients were dying for technology that was not available here but was available elsewhere," said Dr. Robert Saeid Farivar, a cardiothoracic surgeon and one of the foundation's principal investigators.

Twitter: @_JoeCarlson