'Murder-suicide note' found at bloody scene where a young family of five were found dead from gunshot wounds... And a pistol lay next to one of the parents

A murder-suicide note was found at the bloody scene where a young family of five were shot dead in Pennsylvania, police have said.

Parents Mark Short, 44, and Megan, 33, and their children Liana, eight, Mark Jr, five, Willow, two, were all discovered with fatal gunshot wounds.

Police also found a handgun near one of the parents but they refused to say which one - or who they believed was the shooter. 

'This is an apparent tragic domestic incident,' District Attorney John Adams confirmed.

It has emerged that the youngest child Willow had undergone a pioneering heart transplant at one week old.

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Willow Short (pictured) had survived a heart-transplant for two years before she was killed along with her parents and two siblings in an apparent murder-suicide on Saturday

 The Short family, above, (from left) Megan, husband Mark, and children Willow, Liana and Mark, were all found dead at their Sinking Spring, Pennsylvania home with gunshot wounds

She survived the transplant for two years before the family was found dead on Saturday in their Sinking Spring home.

The grisly scene was discovered in the small town in Berks County on Winding Brook Drive in the Brookfield Manor subdivision, according to ABC 6.

The killings happened sometime on Saturday afternoon and the bodies of the parents and three children were discovered around 3pm in the living room.

Police went to the home to check on the welfare of the family after receiving a call from a relative concerned that the woman had not shown up for a lunch date.  

A handgun was found near one of the adults, however authorities did not say which one or who they believe was the shooter. A dog also was found dead.

The family appeared happy in Facebook photos (the father and children pictured above) and a neighbor said: 'I never would have suspected there were any issues'

A handwritten note that 'appeared to be a "murder-suicide" note' was found in the family's Sinking Spring home Saturday afternoon, District Attorney John Adams said.

The district attorney's office said the married couple had been having 'domestic issues.'

'This is an apparent tragic domestic incident,' Adams said on Sunday. 

'Our thoughts and prayers go out to the families at this difficult time.' 

The Berks County District Attorney's office is leading an investigation into the deaths with assistance from police from Sinking Spring and Spring Township. 

The family had previously been featured in articles in The Reading Eagle and The New York Times about Willow's condition, and their difficulties obtaining anti-rejection medication for her.

The murder suicide happened in at their home (above) in the Brookfield Manor subdivision in Berks County

Megan Short often wrote about the struggles her family faced with getting the drug on a Facebook page for The Waiting List.

In a story published in October 2014 in The Reading Eagle, Willow was then five months old and had undergone the heart transplant, her condition was improving.

The story detailed her heart journey from her birth on May 6, 2014 at the Children's Hospital of Philadelphia.

She had suffered from a variation of hypoplastic left heart syndrome, a rare congenital birth defect, according to the newspaper.

During her mother's pregnancy, her parents learned their daughter's heart was not fully formed and could not pump blood efficiently, threatening her life.

Willow had undergone a heart transplant when she was just six days old. Her family had been featured in news articles about her condition and their difficulties obtaining anti-rejection medication for her

When Willow was three days old, she underwent her first open-heart surgery as doctors worked to repair her left ventricle and redirect her circulation.

During surgery, doctors found a tunnel defect and following the procedure, she bled so much she required 16 blood transfusions.  

She was placed on a heart-and-lung bypass machine and was added to the National Transplant List, with her survival depending on a donation of another baby's heart.

The parents were told there could be a three-to-six month wait and prepared for their baby girl to not survive the wait.

However, three-and-a-half days later when Willow was six days old, another heart became available and she went into surgery.

The transplant was described as a 'remarkable success' and by May 29, Willow's heart was working so well doctors removed her from oxygen.

Her mother pictured above holding her for the first time post-transplant - the mother's second time ever holding her baby girl

She was released on June 26, 2014, according to The Reading Eagle.

At the time of her transplant, Willow was one of just three infants to have a heart transplant that year at Children's Hospital of Philadelphia by July 31, 2014.

American doctors have successfully performed infant heart transplants since the mid-1980s, however the procedures are rare, the newspaper reported. 

In 2014, only 64 babies under the age of one had received a heart transplant through July 31, according to the Organ Procurement and Transplantation Network. 

Nearly a year after Willow's transplant, Megan Short wrote a post on The Waiting List of one of her memories.

'Willow's first wail was the most beautiful sound I had ever heard, but it didn't take long before she was intubated within hours of her birth and I could no longer hear her voice,' the mother-of-three wrote. 

'It was so difficult to see her upset. But not be able to hear her cry, it was heartbreaking. 

The family created the Facebook page Willow's Heart Journey, where they posted frequent updates about Willow's condition following the transplant (one shown above from May)

'After her transplant, doctors were able to remove the breathing tube. 

'Hearing her voice and seeing her face without all the tape is one of my favorite memories.'

The family also created a Facebook page, Willow's Heart Journey, where the mother posted frequent updates about Willow's condition following the transplant.

In the 'About' section, she wrote: 'This has been a hard road, but this little miracle has taught me more in her short time than I had learned my entire life before her.

'My faith in God is stronger, my faith in others is renewed, and my love for my family is deeper than ever.

'The strength of this small child has shown me my own.

'Be like the willow tree... able to bend without breaking under the weight of the storms that come your way.'

The last post on the Facebook page was dated May 27 and said Willow had a zero-rejection grade.

Posts just two days before that mentioned Willow was going to have her annual cath and biopsy to check her heart function and pressures, look at her coronary arteries and test for rejection.

Earlier in May, a post on the Facebook page mentioned Willow was 'doing wonderfully' and was in 'great health'

In May, the mother also wrote as they celebrated Willow's second birthday and mentioned she was in 'great health.'

'I haven't posted in quite awhile. Willow is doing wonderfully, in great health and a complete joy,' she wrote.

The day the birthday celebration, the mother shared a snap of Willow in a red and white polka dot dress who also wore Minnie Mouse ears.

She was standing behind her two-layered Minnie Mouse-themed house. 

'Time flies! Miss Willow is 2,' she wrote. 

'As we go into Mother's Day, my mind is on the mother who made the decision to donate her baby's organs,' she continued.

'I am so sorry that your baby is not with you now, but I hope it brings you some peace to know that we are so grateful for the time you have given us with her. 

'I am sure Mother's Day is especially hard for you. 

'We received the call the day after Mother's Day 2 years ago. There are no words to express how thankful we are for your decision.'

Willow pictured above celebrating her second birthday on May 6 while wearing T a red and white polka dot dress while wearing Minnie Mouse ears

 The day after her birthday, Megan Short wrote about how she was thinking about the mother who made the decision to donate her baby's organs

Earlier posts on the Facebook page detail Willow's condition from some of her anti-rejection levels being too high to battling pneumonia, viruses, fevers and infections.

Other posts gave updates celebrating time would go by without Willow having any hospitalizations or cardiology visits.

In a July 2015 story published in The New York Times, it detailed the family's struggle with getting medication for Willow.

At the time of the story was published, Megan Short was 32 years old and Willow was a year old.

The article talked about how Willow could not afford to miss a single dose of a drug she took daily to prevent her body from rejecting her recently transplanted heart.

However, it noted that due to rules from the family's drug plan and the pharmacy, the mother could not order a refill until Willow's monthly supply was three-quarters gone.

But to process a refill, the article said it took about seven days which was risky because it was hard to know whether a new shipment would arrive before the old one ran out.

'You just feel like every month, you're hoping that they don't mess it up,' Short told the newspaper, which went on to focus on the concept of a 'specialty pharmacy.'

The newspaper described the concept as 'a new breed of drug dispensary that has arisen to handle the exploding number of medicines that cost tens or hundreds of thousands of dollars a year and are used to treat complex or rare diseases.'

The story included a photo of the family as they released balloons that May to celebrate the first anniversary of Willow's heart transplant. 

Along with documenting her experience with having a child with a heart transplant, Megan Short also described her struggles with post traumatic stress disorder (PTSD).

In one Facebook post, Mark even wrote that his wife was 'still the most beautiful girl that I've ever met'

The mother wrote in a blog post in April about how having a child born with a severe congenital heart defect was the most significant shift of her life.

She wrote: 'I was so focused on learning everything I could to keep my child alive and to minimize the impact on my other children that I didn't see the full impact that it had on me.'

She described her anxieties over being able to care for her child without doctors and nurses by her side at home and getting used to giving Willow 15 different medicines around the clock.

She also said she suffered from 'anxiety and nightmares' triggered by smells, hallways or even the beeping sound of a phone. 

'I remember sitting up at night just watching her sleep because I was terrified that I placed her NG tube in her lungs and was slowly drowning her,' she wrote.

'I then isolated myself from the world worried that any little germ would kill her.' 

In this September 2014, photo, Willow Short is pictured center at four months old, along with her parents Megan and Mark and sister then six-year-old sister Liana and three-year-old brother Mark

The mother noted she experienced 'survivor's guilt' when children with similar problems from other families passed away.   

However, she said with time things got easier as she became more confident in the medical aspect of caring for Willow, but noted the trauma never goes away.

She described having nightmares and triggering events, noting it took her nearly two years to recognized how she was impacted by these experiences. 

'I don't think PTSD ever truly goes away but, with therapy, medication, and the right support, I have begun to loosen its grip on me,' she wrote.

'As I work on my own mental healing, I wanted to share my experience so that other heart parents know they are not alone.' 

According to The Reading Eagle, the couple had been advocates for organ donation since 2012.  

The father, mother, and their three young children were all killed in what police said was a murder suicide. Authorities have not said who fired the fatal shots

Police and stunned neighbors were at the scene late into the night - the bodies were discovered around 3pm Saturday

Following the deaths on Saturday, a neighbor told The Reading Eagle they 'never would've suspected there were any issues.'

'She's still the most beautiful girl that I've ever met. I'm the luckiest guy in the world to have her as my wife and the mother of my three amazing children!' Mark wrote in December on Facebook about his wife.  

The family lived in a four bedroom, two-and-a-half bath home worth more $400,000, according to Heavy.

Brookfield Manor is an upscale subdivision of detached, single family residences.