More people in North Texas are surviving the No. 1 killer of Americans -- cardiac arrest.
According to a study from UT Southwestern Medical Center, survival rates in Dallas County in the last six years improved by more than 100 percent.
"I'm ecstatic. I didn't know we could do this, really," said Dr. Ahamed Idris, director of the hospital's Dallas Fort Worth Center of Resuscitation Research.
Middle school gym teacher Derrick Ephraim, 41, said he knows you never know when it's coming.
"It just snuck up on me," he said. "I never saw it coming. I was just in disbelief. I couldn't believe it."
Emergency responders on the ground are helping to pump up the numbers. The study trained crews to improve CPR on victims by focusing on chest compressions at the right rate. Responders also use metronomes to help them.
"What this metronome does is help the firefighters keep the right rate," Idris said. "If do they do chest compressions and follow the beeps, they'll be doing chest compressions at the highest survival rate possible."
Mesquite emergency responders are participating in the study.
Last year, the city's survival rate went up four times what it was in 2006.
"Time is muscle," Mesquite Fire Lt. Tash Even said. "And the quicker we can respond and the quicker we can do the chest compressions, the greater chance of survival they had."
Emergency responders and doctors hope to double the survival rate.
They say another key is having regular people learn basic bystander CPR.
A bystander helped Ephraim before paramedics came.
"The doctors told me if they weren't there at that moment, I would have never made it," he said.
Carrollton, Dallas and Irving also participated in the study.