Heart failure affects millions of people worldwide, but treatment options are limited: If patients in advanced stages of the disease can’t get transplants, doctors can implant devices that help the heart pump blood. But those devices put patients at risk for infection and clotting, thanks to valves and pumps that come into direct contact with blood. Now, scientists have created a soft, robotic sheath that may someday help struggling hearts keep beating without that danger (see video above). Made from material that resembles the outer layers of heart tissue, the sheath encases the heart and helps it pump by applying alternating pressure and suction. Building on similar research designs moving through preclinical development, this version uses an array of actuators that function as artificial muscles to squeeze and twist simultaneously. Signals from a pacemaker wire tells the sheath when and how to move, directing it to mimic the weakened heart’s natural rhythm. In pigs whose failing hearts beat at only 47% of control levels, the devices restored heart function to 97%, the researchers report today in Science Translational Medicine. The sheath is still far from human use—safety testing and other tweaks will require a lot more work—but scientists say the study lays the foundation for squeezing more out of heart treatment in the future.