A pacemaker that regulates the heart by wirelessly zapping it with pulses of ultrasound from outside the organ is currently undergoing human trials in Europe.

Conventional pacemakers stimulate the heart tissue via electrical leads that are fed into the heart through a vein. But leads can fail, requiring additional surgery to remove and replace them. The conventional approach also restricts where the therapeutic shock can be delivered.

The new device uses focused acoustic waves that are picked up by a small receiver implanted permanently inside the heart, converting the energy into electricity. Unlike radio waves, ultrasound can pass through tissue at high-enough energy levels without causing any heating.

“This represents a significant breakthrough, eliminating the lead in the heart,” says Paul Skjefte, marketing strategist for EBR Systems, the company that created the pacemaker. The startup, based in Sunnyvale, California, was spun out of research by founder Debra Echt, a former professor of medicine and a cardiologist at Vanderbilt University.

The new device, called the wireless cardiac stimulation (WiCS) system, works like an RFID tag in that the receiver has no power supply of its own, and instead gets all its power and signal wirelessly, but with ultrasound instead of radio waves, says Andy Diston, head of global medical technology practice at U.K.-based Cambridge Consultants, which has partnered with EBR Systems to help commercialize the technology. “The receiver is tiny, about 10 millimeters long and one millimeter in diameter. It’s like a grain of rice and entirely passive. It gets its energy from the transmitter,” he says.

The ultrasonic signal comes from a pacemaker-like box implanted in the chest above the ribs. The box contains an array of ultrasonic transducers that steer and focus the beam toward the receiver. The receiver picks up the signal and converts it into an electrical signal that regulates the heart.