Researchers from Johns Hopkins Medical Institutions have successfully implanted genetically engineered human embryonic stem (ES) cells into the hearts of guinea pigs (Circulation, Vol 432, No 7015).

If replicated in humans, the technique could replace electronic pacemakers used by hundreds of thousands of people worldwide. These devices are used to rectify certain heart conditions that interfere with a normal heartbeat. But they can't react the way the heart's own pacemaker does