PLANO, Texas — Twin sisters Christy and Riley Winkler are inseparable, and that's the way they like it. The sophomores play volleyball and they practice at Plano Senior High School.

Thursday morning they were waiting for the school bus to pull out of the parking lot when Riley saw an adult volunteer collapse, Riley ran to help. "My instinct was to go with her because I'm with her all the time," Christy Winkler said.

Two coaches started CPR. The woman wasn't breathing and didn't have a heartbeat. Christy and Riley knew they needed an AED, Automated External Defibrillators, and knew one was inside the school. "That was one of the main focus uses was that you have to get the AED because that's one of the only things that can really save somebody in that situation to provide the shock you need," Riley Winkler said.

"We knew that was the one thing we needed to focus on getting and get prepared and set up for the people that were doing CPR," Christy said.

Their plan worked. Minutes later the woman was in an ambulance on the way to the hospital. Plano police said she's alive thanks to their quick thinking. "They were able to stay so calm cool and collected during it that they didn't freak. They handled it like a true professional as a hero -- what I've called all of them," said Plano Police Officer Buddy Smith.

The 15-year-old girls didn't make it to class that day. They were supposed to be in Health Class where they were supposed to learn CPR. "Just knowing she's okay, I think that is the main part, the whole focus on why everybody did what they did just to make sure that in the end it was going to be okay," Riley said.