The US state of Tennessee has executed an inmate despite concerns that a heart implant would shock him back to life, potentially causing extreme pain during the lethal injection.
Byron Black, 69, convicted of a triple homicide in 1989, was pronounced dead at 10:43 local time (16:43 BST) at the Riverbend Maximum Security Institution in Nashville, prison officials said.
The US constitution bars cruel punishment, and Black's lawyers had argued that executing him without deactivating the defibrillator would cause a prolonged and painful death.
Seven media witnesses present reported that Black appeared to groan in pain during the process. At one point, he was heard saying: "It's hurting so bad."
It is not yet clear what caused the apparent pain. Black's attorneys have said they will review the data kept by the device as part of the autopsy.
