If a picture is worth a thousand words, the photos and videos taken at the University of Minnesota’s Visible Heart Lab (VHL) are worth millions. It’s the world’s only laboratory where researchers, scientists, doctors, and students can see how medical devices perform inside a beating human heart.

“The advances in product design and anatomic understanding made over the past 28 years in this lab have had the most profound impact of anything I’ve ever done at Medtronic,” said Tim Laske, vice president of research in the Medtronic Cardiac Ablation Solutions Operating Unit, and co-founder of the VHL.

Reanimating hearts: how it works

At the VHL, University of Minnesota researchers -- working with Medtronic scientists and engineers – implant and test heart device prototypes and products inside beating human hearts.

Scientists use a patented, complex combination of pumps, oxygenators and tubing to briefly bring donated hearts back to life. Human hearts generally beat four to six hours in the lab, so research must happen quickly and at any hour of the day.

The hearts pump a special liquid with characteristics similar to human blood. But the liquid is clear, allowing cameras to record everything.

“Instead of imagining how our devices perform within the heart, we can directly visualize their performance and behaviors,” Laske said. “It has taken our ability to design medical devices to a completely new level.”

The result is some of the most important heart device research in the world.

Historic medical device research

Thousands of Medtronic medical devices and prototypes have undergone testing at the VHL since it was founded in 1997.

Among the many experiments, scientists studied cardiac ablation techniques, transcatheter heart valves, leads, catheters, stents, and pacemakers. They’re examining the next generation of pacemakers and our latest ablation technology there today.

The VHL has reanimated thousands of pig hearts over the last 28 years, but the lab’s work on human hearts is especially impactful. As of January 2025, the lab has studied 850 human hearts and reanimated 98.

Human hearts that come to the VHL often arrive through LifeSource, a non-profit that coordinates organ donation for the Upper Midwest.

“There are some good animal models for human hearts, but there’s nothing like the real human heart,” said Dr. Paul Iaizzo, the lab director who co-founded the VHL with Laske in 1997.

The world’s leading heart surgeons and researchers regularly visit the lab to share information, evaluate device prototypes, or simply see how the heart works. Sometimes what they learn changes the nature of the profession.

“It’s mind blowing for us when a pioneer in pacing and electrophysiology tells us ‘the textbooks are all wrong’ after seeing how the heart works from the inside,” Laske said. “The lab has truly redefined the medical community’s knowledge of human cardiac anatomy.”

Iconic past, visionary future

The VHL is in the basement of a University of Minnesota building and in the same room where Medtronic co-founder Earl Bakken invented the first wearable, external pacemaker. In his later years, Bakken regularly visited the VHL.

An iconic Saturday Evening Post photograph from the late 1950s, showing a little boy kept alive by that first device, is on display outside the lab entrance

All the anatomical findings from the lab, including photos and videos, are available to anyone on the VHL website. After 28 years of research, the lab is busier than ever – so it’s likely more heart history will be written there in the years ahead.

“We’re really at the tip of the iceberg in terms of understanding cardiac function,” Laske added. “We’re just beginning to learn how and why the heart functions as it does.”

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