The prognosis of pulmonary arterial hypertension (WHO Group I) has an "untreated" median survival of 2–3 years from time of diagnosis, with the cause of death usually being right ventricular failure (cor pulmonale). A recent outcome study of those patients who had started treatment with bosentan (Tracleer) showed that 89% patients were alive at 2 years. With new therapies, survival rates are increasing. For 2,635 patients enrolled in The Registry to Evaluate Early and Long-term Pulmonary Arterial Hypertension Disease Management (REVEAL Registry) from March 2006 to December 2009, 1-, 3-, 5-, and 7-year survival rates were 85%, 68%, 57%, and 49%, respectively. For patients with idiopathic/familial PAH, survival rates were 91%, 74%, 65%, and 59%. Levels of mortality are very high in pregnant women with severe pulmonary arterial hypertension (WHO Group I). Pregnancy is sometimes described as contraindicated in these women.

The epidemiology of IPAH is about 125–150 deaths per year in the U.S., and worldwide the incidence is similar to the U.S. at 4 cases per million. However, in parts of Europe (France) indications are 6 cases per million of IPAH. Females have a higher incidence rate than males (2–9:1).

Other forms of PH are far more common. In systemic scleroderma, the incidence has been estimated to be 8 to 12% of all patients; in rheumatoid arthritis it is rare. However, in systemic lupus erythematosus it is 4 to 14%, and in sickle cell disease, it ranges from 20 to 40%. Up to 4% of people who suffer a pulmonary embolism go on to develop chronic thromboembolic disease including pulmonary hypertension. A small percentage of patients with COPD develop pulmonary hypertension with no other disease to explain the high pressure. On the other hand, obesity-hypoventilation syndrome is very commonly associated with right heart failure due to pulmonary hypertension.

Following diagnosis, mean survival of patients with PPH is 15 months. The survival of those with cirrhosis is sharply curtailed by PPH but can be significantly extended by both medical therapy and liver transplantation, provided the patient remains eligible.

Eligibility for transplantation is generally related to mean pulmonary artery pressure (PAP). Given the fear that those PPH patients with high PAP will suffer right heart failure following the stress of post-transplant reperfusion or in the immediate perioperative period, patients are typically risk-stratified based on mean PAP. Indeed, the operation-related mortality rate is greater than 50% when pre-operative mean PAP values lie between 35 and 50 mm Hg; if mean PAP exceeds 40-45, transplantation is associated with a perioperative mortality of 70-80% (in those cases without preoperative medical therapy). Patients, then, are considered to have a high risk of perioperative death once their mean PAP exceeds 35 mm_Hg.

Survival is best inferred from published institutional experiences. At one institution, without treatment, 1-year survival was 46% and 5-year survival was 14%. With medical therapy, 1-year survival was 88% and 5-year survival was 55%. Survival at 5 years with medical therapy followed by liver transplantation was 67%. At another institution, of the 67 patients with PPH from 1652 total cirrhotics evaluated for transplant, half (34) were placed on the waiting list. Of these, 16 (48%) were transplanted at a time when 25% of all patients who underwent full evaluation received new livers, meaning the diagnosis of PPH made a patient twice as likely to be transplanted, once on the waiting list. Of those listed for transplant with PPH, 11 (33%) were eventually removed because of PPH, and 5 (15%) died on the waitlist. Of the 16 transplanted patients with PPH, 11 (69%) survived for more than a year after transplant, at a time when overall one-year survival in that center was 86.4%. The three year post-transplant survival for patients with PPH was 62.5% when it was 81.02% overall at this institution.

CTEPH is an orphan disease with an estimated incidence of 5 cases per million, but it is likely that CTEPH is under-diagnosed as symptoms are non-specific. Although a cumulative incidence of CTEPH between 0.1% and 9.1% within the first 2 years after a symptomatic PE has been reported, it is currently unclear whether acute symptomatic PE begets CTEPH. Routine screening for CTEPH after PE is not recommended because a significant number of CTEPH cases develops in the absence of previous acute symptomatic PE. In addition, approximately 25% of patients with CTEPH do not present with a clinical history of acute PE. The median age of patients at diagnosis is 63 years (there is a wide age range, but paediatric cases are rare), and both genders are equally affected.

Portopulmonary hypertension (PPH) is defined by the coexistence of portal and pulmonary hypertension. PPH is a serious complication of liver disease, present in 0.25 to 4% of all patients suffering from cirrhosis. Once an absolute contraindication to liver transplantation, it is no longer, thanks to rapid advances in the treatment of this condition. Today, PPH is comorbid in 4-6% of those referred for a liver transplant.

Historically the prognosis for patients with untreated CTEPH was poor, with a 5-year survival of 40 mmHg at presentation. More contemporary data from the European CTEPH registry have demonstrated a 70% 3-year survival in patients with CTEPH who do not undergo the surgical procedure of pulmonary endarterectomy (PEA). Recent data from an international CTEPH registry demonstrate that mortality in CTEPH is associated with New York Heart Association (NYHA) functional class IV, increased right atrial pressure, and a history of cancer. Furthermore, comorbidities such as coronary disease, left heart failure, and chronic obstructive pulmonary disease (COPD) are risk factors for mortality.

Smoking does not directly cause high blood pressure. However it is a known risk factor for other serious cardiovascular disease.

It has been suggested that vitamin D deficiency is associated with cardiovascular risk factors. It has been observed that individuals with a vitamin D deficiency have higher systolic and diastolic blood pressures than average. Vitamin D inhibits renin secretion and its activity, it therefore acts as a "negative endocrine regulator of the renin-angiotensin system". Hence, a deficiency in vitamin D leads to an increase in renin secretion. This is one possible mechanism of explaining the observed link between hypertension and vitamin D levels in the blood plasma.

Also, some authorities claim that potassium might both prevent and treat hypertension.

Bilharzial cor pulmonale is the condition of right sided heart failure secondary to fibrosis and sclerosis of the pulmonary artery branches. It results from shifting of the "Schistosoma haematobium" ova from the pelvic and vescial plexus to the pulmonary artery branches where they settle and produce granuloma and fibrosis.

Bilharzial cor pulmonale occurs in "Schistosoma mansoni", when the portal pressure rises more than the systemic pressure. So blood will pass from the portal circulation to the systemic circulation carrying "Schistosoma mansoni" ova to reach the lungs.

This condition leads to Pulmonary hypertension, right ventricular hypertrophy and failure.

Hypertension results from a complex interaction of genes and environmental factors. Numerous common genetic variants with small effects on blood pressure have been identified as well as some rare genetic variants with large effects on blood pressure. Also, genome-wide association studies (GWAS) have identified 35 genetic loci related to blood pressure; 12 of these genetic loci influencing blood pressure were newly found. Sentinel SNP for each new genetic loci identified has shown an association with DNA methylation at multiple nearby Cpg sites. These sentinel SNP are located within genes related to vascular smooth muscle and renal function. DNA methylation might affect in some way linking common genetic variation to multiple phenotypes even though mechanisms underlying these associations are not understood. Single variant test performed in this study for the 35 sentinel SNP (known and new) showed that genetic variants singly or in aggregate contribute to risk of clinical phenotypes related to high blood pressure.

Blood pressure rises with aging and the risk of becoming hypertensive in later life is considerable. Several environmental factors influence blood pressure. High salt intake raises the blood pressure in salt sensitive individuals; lack of exercise, obesity, and depression can play a role in individual cases. The possible role of other factors such as caffeine consumption, and vitamin D deficiency are less clear. Insulin resistance, which is common in obesity and is a component of syndrome X (or the metabolic syndrome), is also thought to contribute to hypertension. One review suggests that sugar may play an important role in hypertension and salt is just an innocent bystander.

Events in early life, such as low birth weight, maternal smoking, and lack of breastfeeding may be risk factors for adult essential hypertension, although the mechanisms linking these exposures to adult hypertension remain unclear. An increased rate of high blood urea has been found in untreated people with hypertensive in comparison with people with normal blood pressure, although it is uncertain whether the former plays a causal role or is subsidiary to poor kidney function. Average blood pressure may be higher in the winter than in the summer.

Mild disease has a risk of death of about 10% while moderate disease has a risk of death of 20%. When it occurs as a result of bone marrow transplant and multiorgan failure is present, the risk of death is greater than 80%.

Secondary hypertension results from an identifiable cause. Kidney disease is the most common secondary cause of hypertension. Hypertension can also be caused by endocrine conditions, such as Cushing's syndrome, hyperthyroidism, hypothyroidism, acromegaly, Conn's syndrome or hyperaldosteronism, renal artery stenosis (from atherosclerosis or fibromuscular dysplasia), hyperparathyroidism, and pheochromocytoma. Other causes of secondary hypertension include obesity, sleep apnea, pregnancy, coarctation of the aorta, excessive eating of liquorice, excessive drinking of alcohol, and certain prescription medicines, herbal remedies, and illegal drugs such as cocaine and methamphetamine. Arsenic exposure through drinking water has been shown to correlate with elevated blood pressure.

Portal hypertension is hypertension (high blood pressure) in the hepatic portal system – made up of the portal vein and its branches, that drain from most of the intestines to the liver. Portal hypertension is defined as a hepatic venous pressure gradient. Cirrhosis (a form of chronic liver failure) is the most common cause of portal hypertension; other, less frequent causes are therefore grouped as non-cirrhotic portal hypertension. When it becomes severe enough to cause symptoms or complications, treatment may be given to decrease portal hypertension itself or to manage its complications.

It is sometimes treated with surgery, which involves rerouting blood from the right atrium into the left atrium with a patch or use of the Warden procedure. However, interest is increasing in catheter-based interventional approaches, as well as medical therapy for less severe cases.

The intrahepatic shunts found in large dog breeds are passed on in a simple autosomal recessive way, while the extrahepatic shunts of the small breeds are inherited on a polygenic basis.

Anomalous pulmonary venous connection (or anomalous pulmonary venous drainage or anomalous pulmonary venous return) is a congenital defect of the pulmonary veins.

Non-cirrhotic portal fibrosis (NCPF) is a chronic liver disease and type of non-cirrhotic portal hypertension (NCPH).

Signs and symptoms of portal hypertension include:

In addition, a widened portal vein as seen on a CT scan or MRI may raise the suspicion about portal hypertension. A cutoff of 13 mm is widely used in this regard, but the diameter is often larger than this is in normal individuals as well.

It is characterized by 'obliterative portovenopathy', which leads to various problems such as portal hypertension, massive splenomegaly, and variceal bleeding. It is estimated that about 85% of people with NCPF have repeated episodes of variceal bleeding.

Causes can include pancreatitis, cirrhosis, diverticulitis, and cholangiocarcinoma. It is also a known complication of splenectomy.

Portal vein thrombosis, previously known as Cauchois–Eppinger–Frugoni syndrome, is a form of venous thrombosis affecting the hepatic portal vein, which can lead to portal hypertension and reduction in the blood supply to the liver.

Several studies have attempted to predict the survival of patients with Budd–Chiari syndrome. In general, nearly 2/3 of patients with Budd–Chiari are alive at 10 years. Important negative prognostic indicators include ascites, encephalopathy, elevated Child-Pugh scores, elevated prothrombin time, and altered serum levels of various substances (sodium, creatinine, albumin, and bilirubin). Survival is also highly dependent on the underlying cause of the Budd–Chiari syndrome. For example, a patient with an underlying myeloproliferative disorder may progress to acute leukemia, independently of Budd–Chiari syndrome.

Thrombosis prevention is initiated with assessing the risk for its development. Some people have a higher risk of developing thrombosis and its possible development into thromboembolism. Some of these risk factors are related to inflammation. "Virchow's triad" has been suggested to describe the three factors necessary for the formation of thrombosis: stasis of blood, vessel wall injury, and altered blood coagulation. Some risk factors predispose for venous thrombosis while others increase the risk of arterial thrombosis.

In addition to increasing the risk of kidney cancer, smoking can also contribute to additional renal damage. Smokers are at a significantly increased risk for chronic kidney disease than non-smokers. A history of smoking encourages the progression of diabetic nephropathy.

The cause can be found in more than 80% of patients.

- Primary Budd–Chiari syndrome (75%): thrombosis of the hepatic vein

- Hepatic vein thrombosis is associated with the following in decreasing order of frequency:

2. Polycythemia vera

1. Pregnancy

2. Postpartum state

3. Use of oral contraceptives

4. Paroxysmal nocturnal hemoglobinuria

5. Hepatocellular carcinoma

6. Lupus anticoagulants

- Secondary Budd–Chiari syndrome (25%): compression of the hepatic vein by an outside structure (e.g. a tumor)

Budd–Chiari syndrome is also seen in infections such as tuberculosis, congenital venous webs and occasionally in inferior vena caval stenosis.

Often, the patient is known to have a tendency towards thrombosis, although Budd–Chiari syndrome can also be the first symptom of such a tendency. Examples of genetic tendencies include protein C deficiency, protein S deficiency, the Factor V Leiden mutation, hereditary anti-thrombin deficiency and prothrombin mutation G20210A. An important non-genetic risk factor is the use of estrogen-containing (combined) forms of hormonal contraception. Other risk factors include the antiphospholipid syndrome, aspergillosis, Behçet's disease, dacarbazine, pregnancy, and trauma.

Many patients have Budd–Chiari syndrome as a complication of polycythemia vera (myeloproliferative disease of red blood cells). Patients suffering from paroxysmal nocturnal hemoglobinuria (PNH) appear to be especially at risk for Budd–Chiari syndrome, more than other forms of thrombophilia: up to 39% develop venous thromboses and 12% may acquire Budd-Chiari.

A related condition is veno-occlusive disease, which occurs in recipients of bone marrow transplants as a complication of their medication. Although its mechanism is similar, it is not considered a form of Budd–Chiari syndrome.

Other toxicologic causes of veno-occlusive disease include plant & herbal sources of pyrrolizidine alkaloids such as Borage, Boneset, Coltsfoot, T'u-san-chi, Comfrey, Heliotrope (sunflower seeds), Gordolobo, Germander, and Chaparral.