The chambers of the heart operate as a ‘double-pump’ system for the body’s circulation. In coordination with valves, the chambers work to keep blood flowing in the proper sequence.

BEIJING — Chinese scientists have, for the first time, cultivated a beating heart structure with human cells in a pig embryo, reporting that the heart continued to beat for 21 days unaided.

Doctors say the transplant shows that a heart from a genetically modified animal can function in the human body without immediate rejection.

Surgeons at the University of Maryland Medical Center transplanted a heart from a genetically modified pig into a human patient with terminal heart disease Friday. It was the first successful pig ...