The sleeve - made of material that mimics heart muscle - hugs the outside of the heart and squeezes it, mimicking the action of cardiac muscle.
The early study, published in Science Translational Medicine, shows the concept works on pig hearts.
The British Heart Foundation describes it as a "novel approach" that requires further trials.
Over half a million people in the UK have heart failure.
It is a long-term condition that gradually gets worse over time.
For people with the illness, the heart is unable to pump blood around the body properly - most commonly because cardiac muscle has been damaged, after a heart attack, for example.
Scientists based at Harvard and the Boston Children's Hospital, and in Leeds, say their soft sleeve was inspired by the actions and structure of real heart muscle.
The silicon-based device stiffens or relaxes when inflated with pressurised air.
Fixing it around six pig hearts, scientists found they were able to synchronise the sleeve with each heart's shape and movements.
The study shows the robotic sleeve helped boost the amount of blood being pumped around the body.
And when the hearts stopped beating, the sleeves helped restore blood flow.
Currently, mechanical devices can be implanted in the heart to help it pump. But because they are in direct contact with heart tissue, the body can react to them - leading to the risk of dangerous blood clots.
Researchers argue their sleeve could help cut this risk by "hugging" the outside of the heart rather than being implanted inside it.
But they acknowledge their research is still at an early stage and much longer-term animal studies and then human studies would need to be carried out before it could be used in patients.
Christopher Allen, senior cardiac nurse at the British Heart Foundation, said: "People living with end-stage heart failure are in desperate need of symptom relief, and some will even require a heart transplant.
"We currently don't have enough hearts available to meet the needs of those who require a heart transplant, so we're always looking for innovative new ways to buy time to give people the best chance possible of receiving a new heart and a new lease of life.
"This early research suggests a novel approach to help support heart function, and it will be interesting to see if this translates successfully in human trials in the future."