When Peyton West woke up on Thursday morning he was his usual goofy self. The 13-year-old boy was excited to start his first day of Grade 8 as he posed for a photo on the front steps of his family home in Goshen, Ohio.

With his socks pulled up to his knees, his thick-rimmed glasses and his backpack already on, the adorable young student appeared eager to start the school year in the photo his father took.

What began as a day full of anticipation for the year ahead quickly turned into tragedy when Peyton’s first day of Grade 8 also became his last.

After surviving a heart transplant five months earlier, Peyton collapsed outside of his school’s entrance. He died a short time later in hospital after doctors spent two-and-a-half hours trying to revive him.

Peyton’s family and his doctors still don’t know exactly what happened.

“We don’t know why. We don’t understand it,” Peyton’s dad, Corey West, told WKRC-TV on Tuesday.

There wasn’t any indication that anything was wrong, according to West. He said his son went to bed and woke up the next morning without any problems.

It wasn’t until Peyton’s older brother Ethan dropped him off at school that the boy showed any sign that something was amiss. He told his brother that he wasn’t feeling well right before he collapsed, West said.

Ethan carried his little brother to the school nurse’s office and an ambulance transported him to the Cincinnati Children’s Hospital. The medics told his mother, Melissa West, that Peyton’s heart had stopped.

Half a working heart

Peyton was born with hypoplastic left heart syndrome, a birth defect where the heart’s left ventricle doesn’t develop fully. Multiple heart surgeries are usually required to allow the right ventricle to operate alone.

By the time he was five years old, Peyton had already undergone three surgeries for his heart. He nearly died during that third surgery, according to his father. Despite his health challenges, Peyton always remained upbeat, his family said.

“He was so positive and so happy, and even when he was sick, someone would walk in, and he’d just smile,” West recalled. “He’d just light up a room with his smile.”

The young boy even made headlines in 2013 when he ran on to the field and scored a 65-yard touchdown with the help of his school’s football team and the opposing team.

‘I just wish that he was still alive’

Peyton’s condition worsened in January of this year and his doctors told his parents that he was “teetering on the edge,” West said. A heart became available on March 9 and Peyton underwent the transplant surgery that afternoon.

In the following months, West said Peyton seemed to be feeling better, which is why his sudden death on Thursday came as such a shock to his family.

“I just wish that he was still alive so we could play,” Peyton’s younger brother Nolan said. “I don't know if I can sleep by myself."

Nolan explained that he and Peyton used to share a bedroom and that it can be “scary” sleeping in a room alone.

Peyton’s organs will be donated because it was a heart donation that gave him those extra five months, West said.

Memorial donations can be made out to the Heart Institute at Cincinnati Children’s Hospital, according to Peyton’s obituary.

With files from CNN and WKRC-TV