Bradley Legge suffered massive brain damage after the attack last year in a Portsmouth dental surgery, where he had gone to have two milk teeth removed.
The jury foreman said yesterday they considered he had died from a heart attack because of the anaesthetic and the complication following the cardiac arrest. The foreman said a rare muscle disorder, muscle myopathy, had contributed to the heart attack.
Bradley, from Paulsgrove, Portsmouth, died on 31 October last year, a month after surgery at the Outram Road dental anaesthetic clinic in the city. Home Office pathologist Dr Allen Anscombe told the inquest the boy had been killed by bronco-pneumonia which set in as he lay in a coma.
He said Bradley could have had an existing muscle disorder but anaesthetist Dr Peter Armstrong could not have known about the condition.
The inquest heard Bradley had been admitted to hospital on 24 September after the surgery, but on 12 October doctors allowed him to go home to die. Portsmouth coroner James Kenroy said: "One can only hope that it will always be of some comfort to his family to know that he died surrounded by their love."
Mr Kenroy said evidence was given that Bradley had received unsuitable levels of drugs and electric shocks, but he said Dr Armstrong had "worked desperately hard to save his patient and may well have done all he knew."
He said he would report the outcome of the inquest to the relevant authority to try to prevent other deaths.
After the inquest, Bradley's mother Nikki Legge said her son could have survived. "Evidence was given that he was treated as an adult rather than a child both with regard to the use of drugs and the heart defibrillator," she said.
She said she would be pursuing a claim in the civil courts.