From the outside looking in Lisa Claridge almost looks a picture of good health.

And, just a short year ago she did have enough energy to occasionally play a bit of tennis. But today Ms Claridge pays the price for taking even a short stroll to pick up the morning paper.

"That effort can take me up to 10 minutes to recover."

Sixteen years ago Ms Claridge was diagnosed with the little known heart disease pulmonary hypertension (PH) - high blood pressure in the vessels between the heart and lungs which can lead to heart failure.

Doing a simple physical task most take for granted can leave Ms Claridge feeling exhausted and breathless for many minutes.

In 2004 the Balgownie woman had surgery which successfully removed blood clots from her lungs. The 14-hour surgery gave Ms Claridge a few good years but the illness returned and the 51-year-old's condition has deteriorated over the past seven years.

In March she was diagnosed with a strand of pulmonary arterial hypertension - chronic thromboembolic pulmonary hypertension.

"I've got much worse in the last 12 months because my heart and lungs are working so hard to pump the blood throughout my body that it starts to affect all my other organs," Ms Claridge said.

"Even on blood thinning drugs I've got an illness which unfortunately produces blood clots ... and there's no cure for it.

"I was assessed only two weeks ago at the heart/lung clinic for a transplant and because I get throat clots I'm not a viable recipient.

"The good thing is there are a lot of new drugs which are helping sufferers."

Ms Claridge said World PH Day on May 5 aimed to improve the quality of life and life expectancy of more than 25 million people living with PH worldwide.

The Get Breathless for Pulmonary Hypertension campaign also sought to increase awareness to ensure early diagnosis which helped decrease premature PH-related deaths.

She said there were many types of the disease, which was often hard to diagnose.

PH though was most commonly the result of other health problems - and in Ms Claridge's case it surfaced after a bout of lupus when she was 18-years-old.

"I'm lucky that I have a wonderful GP in Balgownie who has loved having me because he has learned so much about PH that he wasn't aware," she said.

"This campaign is important because many patients spend two to three years seeking an accurate diagnosis."

Information: WorldPHDay.org