- New data shows treadmill tests beat bike tests for accuracy in repaired heart defects
- Helps doctors better track teens and young adults after heart surgery
- Not a new treatment—but changes how we measure heart health
This could change how doctors measure heart strength in young patients born with serious heart defects.
Imagine your child had heart surgery as a baby. Now they’re a teen, feeling fine, playing sports, living normally. But at their check-up, the doctor says, “We need to test how well your heart works during exercise.”
You watch them pedal a bike or walk on a treadmill, breathing into a mask. The numbers come back. But what do they mean? Are they normal? Is the heart keeping up?
For years, doctors didn’t have clear answers—especially for young people born with a complex heart defect called Tetralogy of Fallot (ToF). Even after successful surgery, many face long-term heart strain. Now, a new study gives doctors something they’ve been missing: reliable benchmarks.
Tetralogy of Fallot affects about 1 in 2,000 babies. It’s one of the most common serious heart defects at birth. It means the heart is built wrong—four specific problems that make it hard for oxygen-rich blood to reach the body.
Most babies now survive thanks to early surgery. But “repaired” doesn’t mean “cured.” Over time, many develop leaks in heart valves, especially on the right side. This can weaken the heart muscle and reduce how much energy a person can use during exercise.
That’s where CPET comes in—cardiopulmonary exercise testing. It’s not just a stress test. It measures how well the heart, lungs, and muscles work together when pushed. The key number? VO₂ peak—how much oxygen the body can use during intense effort.
But here’s the problem: doctors didn’t know what “normal” looks like for these patients. And they’ve used treadmills and bike tests almost interchangeably—assuming they give the same results.
They don’t.
The surprising shift
For years, experts thought both exercise tests were equally useful. Same goal: push the patient to their limit. Same measurements. So why not use either?
But this study flips that idea.
Researchers looked at 290 young people—average age just over 20—who had ToF repaired in childhood. All were feeling well. Most were active. None had obvious heart failure.
They did CPET either on a treadmill or a stationary bike. Same lab, same breathing mask, same careful tracking.
The results? Clear and consistent.
On the treadmill, patients used more oxygen—about 10% higher VO₂ peak—than those on the bike. That gap stayed true for both males and females.
This isn’t about effort. It’s about how the body responds.
Walking uphill uses more muscles than pedaling. More muscles = more oxygen demand = a truer picture of heart-lung fitness.
What scientists didn’t expect
Even in healthy hearts, bike tests tend to give slightly lower VO₂ numbers. But in repaired hearts, that difference matters more.
Think of the heart like a car engine. After years of running with a small leak (like a faulty valve), it’s working harder than it should. You need a good test to see if it’s still strong enough for steep hills.
The treadmill is like a steeper hill.
It stresses the system more fully. That’s better for catching small declines before symptoms appear.
This doesn’t mean this treatment is available yet.
How the test tells the story
CPET is like a full tune-up report for the body.
When you exercise, your muscles scream for oxygen. Your heart pumps faster. Your lungs breathe deeper. VO₂ peak is the top speed your body can deliver that oxygen.
Another key number? Oxygen pulse. It’s how much oxygen the heart delivers with each beat. Think of it like fuel per engine cycle. A low number can mean the heart isn’t filling or pumping well.
Then there’s the VE/VCO₂ slope—how efficiently you breathe out carbon dioxide. A high number? A red flag for heart strain.
And OUES—the oxygen uptake efficiency slope—measures how well your body uses oxygen as exercise ramps up. It’s like fuel economy over time.
All these numbers help doctors spot trouble before a patient feels it.
The study included 290 patients, ages 10 to 50, who had repaired ToF and no symptoms. They took CPET tests between 2020 and 2024. Most were active, with normal heart function on MRI scans.
Half did the test on a treadmill, half on a bike. Researchers compared results by age, sex, and activity level.
Treadmill users had higher VO₂ peak—26.4 mL/min/kg vs. 23.0 on the bike. That’s 73% of expected for their age and sex, compared to 62% on the bike.
Oxygen pulse was also higher on the treadmill. Breathing efficiency (OUES) was better. Even the VE/VCO₂ slope—a warning sign when too high—was more favorable.
In short: the treadmill pulled out stronger, more consistent data.
And here’s the catch: many clinics still use bike tests because they’re easier to set up or thought to be more stable.
But for young people with repaired hearts, that might mean underestimating their fitness—or missing early decline.
That’s not the full story.
This study doesn’t change treatment. But it changes how we measure progress.
Right now, doctors often rely on echo tests or MRIs—snapshots of heart structure. CPET adds motion. It shows what the heart does under pressure.
Having sex- and age-specific reference values means doctors can finally say: “Your score is in the normal range for someone like you.”
Before, they guessed.
Now, they can track trends. A slowly dropping VO₂ peak? A rising breathing slope? That could mean it’s time to check the heart valve—even if the patient feels fine.
If you or your child has repaired ToF, this won’t change your care tomorrow.
No new drugs. No new surgeries.
But it could change your next exercise test.
Ask: Are they using a treadmill or a bike? Are they comparing results to the right benchmarks?
And don’t panic if past tests were on a bike. Lower numbers might not mean worse health—just a different test.
Talk to your cardiologist. Bring up CPET. Ask what your VO₂ peak means in context.
The small print
The study has limits.
All patients were feeling well—so results may not apply to those with symptoms. Most were young adults. Kids under 10? We still need data.
And while the treadmill gave higher numbers, we don’t yet know which test predicts long-term outcomes better.
This was also a single-center study. Different labs might see slightly different results.
What happens next
The real win here? Setting a standard.
Now, researchers can build on this. Future studies may track how these CPET numbers change over time—and how they link to real-world outcomes like hospital visits or need for valve replacement.
Pediatric norms are still missing. Multi-center studies are needed. But for the first time, doctors have solid reference points for young adults with repaired ToF—and a clear reason to choose the treadmill when possible.