In the third major deal this summer involving makers of ­transcatheter mitral valves, Medtronic PLC has agreed to pay up to $458 million to acquire an obscure but promising California company called Twelve Inc.

"We have followed the transcatheter mitral valve space closely and firmly believe that Twelve has the most novel technology, along with a strong, proven team," said the president of Minnesota-run Medtronic's coronary and structural heart division, Sean Salmon, in a statement.

The deal, expected to close in October, is aimed at speeding up Medtronic's progress toward a minimally invasive mitral valve by at least two years.

Privately funded Twelve has no website, but it filed a report on in April announcing intentions to enroll 10 patients in Poland in an early clinical trial of its heart device. The still-unnamed device allows a physician to install a new mitral valve deep in the heart by wending a skinny tube called a catheter inside it from a small incision elsewhere in the body.

The market for devices that can repair leaky mitral heart valves without requiring open-heart surgery is predicted to quickly grow into a multibillion-dollar niche. A similar growth trajectory has already been proven with minimally invasive therapies to replace the aortic valve.

Medtronic is one of only two companies that sells minimally invasive aortic valves in the U.S., and it has long been interested in entering the market for mitral valves, which are more difficult for physicians to reach, but potentially more lucrative.

Mitral regurgitation is one of the most common heart diseases in older age, affecting 4 million Americans. The condition affects more than four times the number of people who have aortic stenosis, which is expected to generate as much as $2 billion in sales this year of catheter-delivered aortic valves.

All transcatheter valves are made of special metal that can be folded up inside a narrow tube and then unfurled inside the heart with the use of animated X-rays and manual controls outside the body. The metal frame is like a heart stent with a ­bioprosthetic valve sewn inside to control blood flow between the left atrium and left ventricle.

In March, analysts with Leerink Partners projected that the U.S. has about 300,000 people with functional mitral regurgitation today. Based on a projected average sales price of roughly $30,000 for transcatheter mitral valves, that would translates to $9 billion initial U.S. market.

Larger device companies have taken notice.

On July 31, Roseville-based Tendyne agreed to a $250 million buyout offer from Chicago's Abbott Laboratories, following Tendyne's first-in-U.S. implants earlier this year by doctors from the Minneapolis Heart Institute Foundation. Abbott Labs already makes a mitral-repair device called MitraClip, which is different from replacement valves like Tendyne's.

That deal came two weeks after California-based Edwards Lifesciences, which was first-to-market in aortic valves, agreed to pay up to $400 million for CardiAQ Valve Technologies. Irvine, Calif.-based CardiAQ is enrolling patients in a study of its transcatheter mitral valve.

The news is likely to increase scrutiny of a Canadian company called NeoVasc, which has one of the most-developed mitral-valve replacement devices in the world. Officials with NeoVasc didn't respond Tuesday to a question about whether they've been courted by a Twin Cities devicemaker.

Medtronic already had an in-house mitral valve ­program, which unveiled an early device design about two years ago. On Tuesday, spokeswoman Wendy Dougherty said the acquisition of Twelve will allow it to bring a transcatheter mitral valve to market two to three years sooner than if it had relied on its internal program alone.

"We will be working with regulatory authorities immediately post-close to determine a clinical path forward and will be able to share greater specificity about dates as we integrate the company," Dougherty wrote in e-mail.

Medtronic said it expects to pay nearly half a billion dollars for a company with minimal revenue, and yet not dilute its own earnings projections. "Any cost of acquiring this company won't affect our earnings because we will find ways to offset the costs in other areas of the company," Dougherty wrote.

Medtronic shares declined 1.5 percent Tuesday, to $69.88. The world's largest devicemaker moved to Dublin, Ireland, this year but kept its U.S. headquarters in Fridley.

Little is known publicly about Twelve. It has been called the 12th spinoff company from med-tech start-up incubator the Foundry in Menlo Park, Calif. Funded by several private-equity firms, Twelve announced a successful $35 million equity offering in April in securities filings. No other financials are ­available.

Twelve has a four-word description on the Foundry website: "Transforming mitral valve replacement." Medtronic declined to release an image of the device.

Joe Carlson • 612-673-4779

Twitter: @_JoeCarlson