Ari Schultz, a five-year-old whose struggle with a congenital heart defect went viral, has died just one month after receiving a heart transplant.

The boy died at Boston Children’s Hospital in Massachusetts on Friday night, listening to the Red Sox, his favourite baseball team.

Ari's story made headlines across the world after his parents posted regular messages online about their son’s health struggles, including a two-week coma.

They filmed the boy’s reaction at finding a heart transplant match in March, with thousands viewing the post on his Ari “Danger” Schultz Facebook page.

On their blog Echo of Hope they posted a message saying their son had been admitted to the emergency department and placed on life support. "We called 911 at 4:19 a.m. as Ari was having a seizure," they wrote on Thursday morning.

"Very scary. At the hospital now. Something is going on. We don’t know what."

A few hours later, the five-year-old’s condition deteriorated.

"Just after 10 am Ari coded in the emergency department," read a subsequent post.

"He had over a half an hour of CPR and has been placed on life support in the cardiac intensive care unit. Path forward unknown."

The young boy was born with hydoplastic left heart syndrome and aortic stenosis. His condition was discovered when his mother was 18 weeks pregnant.

He had two successful operations before he was born so he had a four-chamber heart instead of a two-chamber one. During his short life, Ari had undergone over 20 surgeries before receiving a heart transplant.

More than 5,000 heart transplants take place every year, according to UpToDate, a physician-authored clinical decision support resource.

Survival rates and risks are difficult to calculate as the procedure has only been carried out since the mid 1980s.