Pulmonary hypertension is high pressure in the pulmonary artery.

There are 5 major reasons the pressure could be high.

Reason 1 (World Health Organization, WHO, group 1): The blood vessels (arteries) themselves could be a problem. Here the arteries become narrowed, thick and stiff. Think a garden hose where the inner wall continually closes off. When the arteries themselves are an issue its called pulmonary arterial hypertension. Sometimes you may hear a doctor call this primary pulmonary hypertension because the primary problem is the arteries themselves. Treatments involves trying to open up the arteries.

Reason #2 (WHO group 2): The left side of the heart could be struggling. This would backflow blood into the lungs. The backflow of blood in the lungs causes the pressure in the arteries to increase. In this case, the high pressure in the lungs is secondary to (think caused by) the left side heart issue. Treatments involve trying to improve left side heart function.

Reason #3 (WHO group 3): The lungs could have a problem. The lungs could be damaged and not oxygenated blood well, so blood backs up in them. In this category people might have COPD or some other lung disease. Again in this case the high pressure is secondary to the lung disease. Treatments involve trying to improve lung function or relieve the symptoms of the lung disease.

Reason #4 (WHO group 4): The person has a blood clot in the lung. Think a garden hose with a marble in it. In this case, the high pressure is secondary to the clot. Treatments involve trying to break up or remove the clot and prevent any future clots.

Reason #5 (WHO group 5): The person has another disease. In this case the pulmonary hypertension is secondary to their other disease. One example of a disease that can cause PH is sacrododsis. Treatments here involve trying to slow the progression of the other disease.

So, in summary PAH and PH are both high blood pressure in the pulmonary artery. PAH is just a specific group of PH where the high pressure is caused by a problem with the arteries.

Hope this helped.

(There is a difference
(PH) and pulmonary arterial hypertension (PAH). Pulmonary arterial hypertension (PAH) is a specific subgroup of pulmonary hypertension (PH). The definition of PH is more inclusive than the definition of PAH, meaning that the specific hemodynamic measurements used to define PAH do not apply to PH.

Pulmonary hypertension (PH) is simply an elevation in the pressure in the arteries of the lungs. Many diseases such as obstructive sleep apnea (OSA), lung diseases, diastolic heart failure, and diseases of the left heart can cause the pressures in the pulmonary arteries to rise but this does not mean you have pulmonary arterial hypertension (PAH). Pulmonary arterial hypertension is a disease of the blood vessels of the lungs meaning these vessels have changed causing the elevation in pressure. In pulmonary hypertension, the elevation of the pressures is caused by another disease, the blood vessels themselves are not the problem.
*Info via PH website.

Let me tell you that blood clot in the lung. I felt like I had been hit by lightning. Ive had 6 heart attacks. Theres no comparisons. Heart attacks for me everyone of them was completely difference. Ill take them over blood clot anyday. Because Ive had them in my legs to, ill be on blood thinners for ever.

With all my stents and heart attacks they had to assume my lungs were doing the same. For a year prior to diagnoses I complained about the squeezing in my chest.