On Apr. 2, 2025, Northwestern University engineers announced they have developed a pacemaker so tiny that it can fit inside the tip of a syringe — and be non-invasively injected into the body. Although it can work with hearts of all sizes, the pacemaker is particularly well-suited to the tiny, fragile hearts of newborn babies with congenital heart defects.

Smaller than a single grain of rice, the pacemaker is paired with a small, soft, flexible, wireless, wearable device that mounts onto a patient’s chest to control pacing. When the wearable device detects an irregular heartbeat, it automatically shines a light pulse to activate the pacemaker. These short pulses— which penetrate through the patient’s skin, breastbone and muscles — control the pacing.

Designed for patients who only need temporary pacing, the pacemaker simply dissolves after it’s no longer needed. All the pacemaker’s components are biocompatible, so they naturally dissolve into the body’s biofluids, bypassing the need for surgical extraction.

The team used an infrared wavelength of light that penetrates deeply and safely into the body. If the patient’s heart rate drops below a certain rate, the wearable device detects the event and automatically activates a light-emitting diode. The light then flashes on and off at a rate that corresponds to the normal heart rate.

Even though the pacemaker is so tiny — measuring just 1.8 millimeters in width, 3.5 millimeters in length and 1 millimeter in thickness — it still delivers as much stimulation as a full-sized pacemaker.

The technology’s versatility opens a broad range of other possibilities for use in bioelectronic medicines, including helping nerves and bones heal, treating wounds and blocking pain.

The study, published in the journal Nature, demonstrates the device’s efficacy across a series of large and small animal models as well as human hearts from deceased organ donors.