In patent disputes, it's the patent holder—not the accused infringer—who must always bear the burden of proof. That's true even when the parties had struck a licensing deal in the past, the US Supreme Court made clear in a ruling published today.

The case decided was Medtronic, Inc. v. Mirowski Family Ventures. Michel Mirowski and co-inventor Morton Mower were pioneers in the area of implantable heart-stimulation devices (pacemakers). Medtronic paid royalties to Mirowski for some of its products, harking back to its first licensing deal in 1991. But the company said a new generation of devices didn't infringe, and it resisted paying for additional patents Mirowski had acquired in 2003 and 2007.

Mirowski, no surprise, disagreed. The two parties went to court, with Medtronic firing the first shot: a so-called "declaratory judgment" lawsuit saying that it didn't infringe Mirowski's patents.

The situation escalated last year, when the US Court of Appeals for the Federal Circuit, the nation's top patent court, ruled that the burden of proof in that dispute should actually be on Medtronic, not Mirowski, as the lower court had ruled.

Today the Federal Circuit was overruled, in a 9-0 decision written by Justice Stephen Breyer. The burden is always on the patent holder to prove infringement, he explained—even in a situation where in the past, the accused infringer agreed to take a license.

Since patent licensing is so common in the tech sector, the case will have implications beyond the devices at issue. It will generally offer a slight tip of the scales of power, away from companies that want to enforce their patents and in favor of companies that want to challenge those patents.

While it will have an impact on competitors who license patents to each other, it probably won't make much difference in the many battles over the patent-licensing shops called "patent trolls." Most settlements with non-practicing patent holders are onetime, lump sum payments, not ongoing royalties like Medtronic was paying to Mirowski.

Supreme Court patent slapdown has sequels on the way

The situation for licensees that wanted to challenge patents actually used to be much worse. Until 2007, someone who'd agreed to a patent license typically was not allowed to challenge the patents at all; if the patents were agreed to once, essentially, they were agreed to forever.

The situation changed when the Supreme Court stepped in to override the Federal Circuit in the Medimmune v. Genentech case.

But while the Federal Circuit was allowing licensees to challenge patents, as the Supreme Court told it to, in today's decision Breyer noted that the Federal Circuit had allowed Medtronic to have its day in court, but it was still creating a "significant obstacle" and making the process "disadvantageous" for Medtronic.

Today's decision is one of several in recent years in which the Supreme Court has struck down Federal Circuit rules that were seen as too friendly to patent owners.

This first 9-0 decision doesn't bode well for the Federal Circuit. Today's Medtronic case is the first of several big Federal Circuit rulings that the Supreme Court is reviewing. Predicting outcomes is a loser's game, but they presumably didn't take up the cases because they're thrilled with the status quo.

The high court has shown an unprecedented interest in patents this year. There are four more patent cases still to be argued in front of the justices, a remarkable number. There's Alice v. CLS Bank, a case that seeks to bring order out of chaos when it comes to the law around software patents; Limelight v. Akamai, which will resolve questions around "divided infringement;" Nautilus v. Biosig, grappling with what kinds of patents are written too vaguely; and the twin cases Highmark v. Allcare and Octane Fitness v. Icon Health, two cases that are being heard together, which will determine when attorney's fees can be awarded in a patent case.