Abbott Laboratories on Thursday announced a $250 million deal to buy Roseville heart-device maker Tendyne, which features a product in the promising niche of minimally invasive mitral valve replacement.

Tendyne's Bioprosthetic mitral valve can be implanted inside a patient's beating heart through a small tube, avoiding the need for open-heart surgery. Minimally invasive mitral valves are expected to become a multibillion-dollar niche within a decade, though none are yet approved for sale in the U.S.

Illinois-based Abbott expects to close its acquisition of Tendyne by the end of September, pending approval from antitrust regulators. The deal includes a $25 million investment Abbott already made, but not the undisclosed future payments tied to meeting regulatory goals.

Separately on Thursday, Abbott announced an undisclosed investment with an option to acquire a California company called Cephea Valve Technologies, which is also developing a minimally invasive mitral valve replacement therapy.

Tendyne's mitral valves are being studied to treat regurgitation, where blood leaks backward through the valve. As many as 4 million Americans are affected by moderate to severe forms of the condition.

The mitral valve is one of four heart valves that pump blood throughout the body. Investors' strong interest in mitral therapies is rooted in the recent success of minimally invasive replacements of the aortic valve.

In recent years, Minnesota-run Medtronic PLC and California-based Edwards Lifesciences have sold hundreds of millions of dollars worth of minimally invasive aortic valves. Boston Scientific Corp., which has major operations in the Twin Cities, and Little Canada-based St. Jude Medical Inc. are testing their own catheter-delivered aortic valves, and Medtronic is expanding the applications for its existing ones.

So far, aortic valves implanted through catheters are only approved for more frail patients who are not good candidates for open-heart surgery. The procedure avoids the need for open-heart surgery, but physicians are still learning how to get long-term results that are as strong as traditional surgery. Eventually the companies aim to expand the market to less-risky patients as well.

Although mitral-valve diseases represent a larger patient population, minimally invasive therapies for the aortic valve were developed first. "The aortic approach is much easier than the mitral approach," said Dr. Ganesh Raveendran, a University of Minnesota cardiologist who has implanted transcatheter aortic valves.

Tendyne officials couldn't be reached for comment Thursday, but investor handouts from the company quote analysts predicting minimally invasive mitral valve replacements will reach $750 million in sales in 2020 and grow to $3 billion five years later.

In April, the Minneapolis Heart Institute Foundation reported the first successful U.S. implant of a Tendyne valve, which was done at Abbott Northwestern Hospital. "This milestone marks the beginning of a new era of transcatheter valve replacement for patients with malfunctioning mitral valves," said cardiologist and Tendyne study principal investigator Dr. Wesley Pedersen in a news release at the time.

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