From Erector Set to Heart Bypass: How Yale Transformed Cardiac Surgery

In the mid-20th century, cardiac surgery faced a fundamental obstacle: surgeons could not safely stop the heart long enough to repair it. Operations were limited to procedures that could be performed on a beating heart or around it. Complex repairs inside the heart remained largely out of reach.

In 1948, Yale School of Medicine third-year student William H. Sewell Jr. set out to change that. For his graduation thesis, he proposed building a mechanical device that could temporarily take over part of the heart’s function, allowing surgeons to operate while blood continued to circulate.

He reportedly told classmates, “Somebody is going to develop a machine that will bypass blood around the heart. That will open up a whole new field of surgery, and I am going to be a part of it."

Sewell had long been fascinated by how machines worked. As a child, his father gave him an Erector set—a kit of miniature girders, bolts, pulleys, and a small electric motor. It taught him how moving parts could be assembled into functional systems.

Years later at Yale, that early mechanical curiosity resurfaced. Working with William W. L. Glenn, MD, then a young surgeon who would later become chief of cardiothoracic surgery at Yale, Sewell began constructing a bypass pump from readily available materials. He combined an Erector set motor with tubing, a rubber bladder, and inexpensive valves—including components adapted from party noisemakers. The total cost: $24.80.

The result was crude by modern standards—but it worked.

Rather than attempt full heart-lung replacement, Sewell and Glenn pursued a more targeted goal: bypassing only the right side of the heart while allowing the lungs to continue oxygenating the blood.

Early versions using roller pumps failed. Sewell then shifted to a pneumatically powered design that used compressed air to generate sufficient force to move blood through the system.

In a series of experiments conducted at Yale, the pump successfully diverted blood around the right side of a dog’s heart for more than an hour. The animal recovered after the procedure.

The experiment demonstrated that a mechanical device could temporarily sustain circulation while the heart was bypassed—a critical proof of concept at a time when the feasibility of mechanical support remained uncertain.

The original pump is now preserved in the National Museum of American History at the Smithsonian Institution in Washington, D.C.

Sewell’s pump was not the first heart-lung machine, nor was it an implantable artificial heart. But it contributed to a growing body of research showing that extracorporeal circulation—blood flow outside the body—was possible.

Just a few years later, in 1952 and 1953, surgeons elsewhere would perform the first successful open-heart procedures using evolving heart-lung machines. Those systems incorporated lessons from earlier experimental designs, including pneumatic approaches similar to Sewell’s.

Over the following decades, cardiopulmonary bypass machines became standard in open-heart surgery. Today, nearly two million heart surgeries are performed globally each year, including valve repair, coronary bypass grafting, congenital defect correction, and heart transplantation—procedures that depend on the ability to temporarily reroute circulation.

Early mechanical bypass experiments also helped catalyze research into long-term mechanical circulatory support.

In 1982, the first permanent total artificial heart was implanted in Barney Clark, a 61-year-old patient with end-stage heart disease. Clark survived 112 days with the device. While artificial heart technology has evolved significantly since then, the underlying principle—mechanically sustaining circulation—can be traced back to foundational experiments like Sewell’s.

Today, ventricular assist devices (VADs) support patients awaiting transplant or living with advanced heart failure. Mechanical circulatory support has become a core pillar of modern cardiology.

Even as heart-lung machines remain central to cardiac surgery, researchers are exploring ways to reduce reliance on them.

At Yale School of Medicine, surgeons are advancing minimally invasive and robot-assisted techniques that allow certain cardiac procedures to be performed on a beating heart, reducing surgical trauma and recovery time. Researchers are also integrating artificial intelligence into surgical planning and intraoperative decision-making.

The goal is not simply to improve the bypass machine—but, in some cases, to make it unnecessary.

Heart disease remains the leading cause of death worldwide, with enormous human and economic costs. The ability to repair and replace damaged cardiac structures has saved countless lives.

Sewell’s improvised pump—built from toy parts and compressed air—did not solve heart disease. But it helped demonstrate that circulation could be sustained mechanically, opening a path toward modern cardiac surgery.

What began with an Erector set became part of a broader transformation in medicine: proof that life-sustaining systems could be engineered, and that surgery on the human heart could move from impossibility to routine practice.