The only clue? A power pack on his back.
"I don't feel the pump," Stowe said. "I can actually hear it sometimes. There's no pulse, just a continuous flow. You can just hear it revving, sort of. But it's saved my life."
Stowe, a former airline pilot, received his mechanical pump four years ago as part of a clinical trial, after a series of heart attacks left his heart barely pumping.
"I couldn't walk more than a few feet without feeling out of breath."
This new generation of mechanical pump, called Heartmate II, is attached directly to the heart, helping it push blood through the body.
Originally, this pump was supposed to be used in patients only as a stopgap measure until a donor heart became available for transplantation. But it's so small and so effective that the U.S. Food and Drug Administration is now considering approving it as a permanent treatment in older heart-failure patients.
Based on a two-year study of 200 patients that compared Heartmate II to its predecessor, the FDA has granted what is called premarket approval to the device. This means that it can now be used as cardiac support for patients with advanced-stage heart failure who are ineligible for transplantation, rather than just an interim device for those awaiting transplants.
Typically, heart disease is treated only with medications. In severe cases like Stowe's, only 8 percent of patients survive two years. But with the pump, 58 percent of patients are alive two years later.
As part of the premarket approval, the Pleasanton, Calif.-based developer Thoratec must complete a postmarket study and measure adverse effects, functional status, and quality-of-life data associated with the device. But cardiologists are already optimistic.
"If this is approved as a permanent therapy, it could save the lives of 10,000 Americans a year," said Dr. Ulrich Jorde, a cardiologist at NewYork-Presbyterian Hospital.
Other doctors were equally enthused. Dr. Valluvan Jeevanandam, chief of cardiac and thoracic surgery at the University of Chicago Medical Center, called the FDA's move "one of the most important events in the treatment of advanced heart failure." He said that at his institution, the device has largely supplanted heart transplant as the option of choice.
He added that while treatment with medication has been shown to improve the chances of patient survival by about 5 to 10 percent, therapy with the device "has almost tripled survival from 23 to 58 percent. That is remarkable for these very sick patients."
Dr. Jay Pal, assistant professor of cardiothoracic surgery at the University of Texas Health Science Center at San Antonio, agreed that the move is a significant one.
"This new approval will allow us to provide this life-saving treatment to a new population of patients who were previously not candidates for mechanical circulatory support," he said.
Still, some cardiologists said that while the technology is promising, it comes with serious considerations.