Ryan Marquiss' heart also hadn't developed and so he only had half a heart - a combination of defects, which is so rare that he is the only one of his kind in the world.
Doctors advised his devastated parents to terminate the pregnancy when his mother was just 12 weeks pregnant, but they bravely refused.
It is a gamble that has paid off, as Ryan is just about to celebrate his third birthday.
"We wanted to let nature take its course, so we refused to have the termination," the Sun quoted his 34-year-old mother as saying.
"We knew it would be a miracle if he survived the birth but we were unwilling to take matters into our own hands.
"The doctors told us that no baby with Marquiss' combination of defects had ever survived, so the fact that he is here with us today, is just amazing. He really has astounded everyone,' she said.
The incredibly rare defect, ectopia cordis, affects only eight in every million births and ninety percent of these are stillborn or die within three days.
To add to that Marquiss was also suffering from hypoplastic right heart syndrome, where only the left side of the heart had developed properly.
"All the odds were stacked against him," the mum, who lives with husband Henry, and their other children in Pennsylvania, USA, said.
"We knew that it was a miracle that he had been born alive with his heart outside his body, but then to have another life-threatening condition of only having half a heart meant that everything was against him surviving," she added.
Doctors at the Children's National Medical Centre in Washington delivered him at the end of February 2009 by caesarian, helped by a team of 30 medical professionals.
"If he survived the birth his exposed heart likely would become infected and kill him," Dr Mary Donofrio, Director of the fetal heart programme at the Children's National Medical Centre said.
"Even if infection didn't happen his heart had one working ventricle and he would require open heart surgery to rewire the blood flow through it.
"I told the family right from the start that if he survived, it was a miracle," she said.
Marquiss had to have an operation at just two weeks old to have a central shunt placed in his heart to ensure proper blood flow.
Then he underwent more than a dozen operations over the next two years. He had operations to replumb his heart so that the half a heart would do the job of a full size heart. Doctors also put tissue expanders under his skin to produce more skin so they could use it to cover his exposed heart.
"He will need some sort of chest protection operation in the future but it may be overcome by just wearing some sort of protective padding when he plays sport. He won't be a competition athlete, but we are hoping he can run around on the playground and climb trees like any other child," his mother said.
Ryan's case has now been reported in a medical journal. Doctors believe that his survival offers hope for other babies with serious heart defects.