Sergeant Roman Colon Jr., an officer with the Boston Municipal Security Department, was on the first floor at City Hall when he heard a loud scream upstairs and started running. A man on the floor had no pulse and was not breathing; Colon then began performing CPR, or cardiopulmonary resuscitation, on him.

“That’s when I saw who he was,’’ said Colon. It was Suffolk County Register of Probate Felix D. Arroyo, who had just gone into cardiac arrest. While doing chest compressions, Colon kept talking to Arroyo in Spanish: “¡Respira, Félix, respira!’’ He then asked someone to get an AED (automatic external defibrillator), which was 20 feet away. Colon used it on Arroyo twice. “Now he had a faint pulse.’’

That was 20 days ago. Today, Arroyo is back to work .

Colon, certainly, is the hero of the story. But so are the officials who recently decided to put an AED on each of the nine floors at City Hall; before last year, there were only two.

Almost 90 percent of those who suffer cardiac arrest out of the hospital die. Chances of survival increase dramatically when someone performs CPR immediately or has access to an AED, which nonmedical personnel can be trained to use.

Yet broad deployment of AEDs remains a challenge. Massachusetts requires them only in health clubs and, starting in July, public schools. New York goes further, requiring them in all public gathering places and in all public buildings. No wonder.