Toddler shot dead just two years after receiving life-saving heart transplant.

A toddler who received a life-saving heart transplant just two years ago has been shot dead in what police say is a suspected murder-suicide.

Found alongside her parents and two older siblings inside their Pennsylvania home on Saturday, Willow Short had received a lifesaving heart transplant in 2014 when she was just one week old.

33-year-old mother Megan, 40-year-old father Mark, and siblings 8-year-old girl Liana and five-year-old boy Mark Jr and the family dog were also pronounced dead at the scene.

Heart transplant baby, Willow Short. Source: Facebook.

According to ABC 6, a handgun and handwritten note were found by authorities.

While local police have said it is still unclear as to who fired the fatal shots, they did confirm parents had ongoing domestic problems.

Police were reportedly called to the scene on Saturday after Megan Short failed to show up to lunch with a relative.

The Short family, Megan, Mark, Liana, Willow and Mark Jr. Source: Facebook.

The Pennsylvanian family first made headlines in 2014 after Willow was born with a congenital heart defect on 6 May 2014.

In the days that followed, Willow underwent open heart surgery and countless blood transfusions just to stay alive. And by 9 May - just three days after being born - she received a transplant.

"Someone else’s child died so that my child could live,” Megan told the Reading Eagle at the time.

Willow Short received a life-saving transplant just three days after being born. Source: Facebook

Sharing their unique experience following her surgery, Megan chronicled Willow's journey on a dedicated Facebook page, last year writing "Willow will be one next week and one year post transplant a week later. It is hard for me to think of where we were last year during this same time. It is even harder to know that during those days her donor was living out the last of his very short life. We are incredibly grateful for this gift." 

Megan's most recent post to the page was on 26 May 2016.