Carcinoid heart disease is a condition in which tumors called carcinoid tumors release hormones that damage the heart’s valves, causing them to stiffen and malfunction. It develops in a subset of people who have carcinoid syndrome, a cluster of symptoms (flushing, diarrhea, wheezing) caused by hormone-secreting neuroendocrine tumors that have typically spread to the liver. Estimates of how many carcinoid syndrome patients develop heart involvement vary widely, from as few as 3% to as many as 65%, depending on how aggressively doctors screen for it.
How Serotonin Damages the Heart Valves
Carcinoid tumors produce serotonin and other vasoactive hormones. When tumors have spread to the liver, these substances drain directly into the bloodstream and travel to the right side of the heart, where they come into contact with the inner lining of the heart valves at high concentrations. Serotonin activates a specific receptor on cells beneath the valve surface, triggering those cells to multiply and produce excess collagen and fibrous tissue. The result is a distinctive white plaque made of smooth muscle cells, collagen, and elastic tissue that coats the valve surface like a layer of scar tissue.
Over time, this plaque thickens, stiffens, and retracts the valve leaflets. Instead of opening and closing smoothly, the leaflets become fixed in a partially open position, unable to seal shut. Blood leaks backward (regurgitation), and in some cases the valve opening narrows (stenosis). The combination steadily increases the workload on the right side of the heart.
Why the Right Side of the Heart Bears the Burden
Nearly all carcinoid heart disease affects the tricuspid and pulmonary valves on the right side of the heart. The reason is straightforward: blood leaving the right heart passes through the lungs, which break down serotonin and other vasoactive substances before they can reach the left-sided valves. The lungs act as a filter, protecting the mitral and aortic valves in most cases.
In a large case series, 97% of patients with cardiac involvement had tricuspid valve disease, and 90% of those had moderate or severe regurgitation. Pulmonary valve disease was present in 88%, with regurgitation in 81% and stenosis in 53%. Left-sided valve involvement does occur on occasion, particularly in patients with very high hormone levels or a rare heart defect that allows blood to cross from the right side to the left without passing through the lungs.
Symptoms to Recognize
Early carcinoid heart disease often produces no symptoms at all, which is why routine screening matters. As valve damage progresses, it leads to right-sided heart failure. The signs are distinct from the chest pain or shortness of breath people associate with typical heart disease:
- Swelling in the legs and ankles from fluid backing up in the veins
- Abdominal swelling (ascites) as fluid accumulates in the belly
- Fatigue and exercise intolerance because the heart can no longer pump blood efficiently through the lungs
- Prominent neck veins visible as pulsing or distension in the jugular area
These symptoms can be easy to attribute to other causes, especially in someone already dealing with cancer-related fatigue and gastrointestinal problems from carcinoid syndrome. That overlap makes echocardiographic screening essential rather than relying on symptoms alone.
How Carcinoid Heart Disease Is Diagnosed
Echocardiography (ultrasound of the heart) is the primary diagnostic tool. Doctors look for a characteristic pattern: valve leaflets that appear thickened and straightened, moving in a stiff, board-like fashion rather than their normal fluid motion. In more advanced cases, the leaflets are visibly retracted and fixed, failing to close together, with a clear gap where blood leaks through. The chords that anchor the valve leaflets to the heart muscle may be fused, shortened, and thickened. In 90% of patients who undergo a more detailed ultrasound from behind the heart (transesophageal echocardiography), carcinoid plaque deposits are visible on the inner wall of the right ventricle.
Three-dimensional echocardiography can reveal additional detail, such as plaque deposited on a single valve cusp or constriction of the valve opening. Cardiac MRI is sometimes used as a complement, particularly when ultrasound images are difficult to obtain.
Blood and Urine Markers
A 24-hour urine test that measures a serotonin byproduct called 5-HIAA is a key part of monitoring. Patients who develop carcinoid heart disease consistently have higher levels than those who don’t. In studies, median urinary 5-HIAA levels in patients with heart involvement ranged from 266 to 1,381 µmol per 24 hours, compared with 67.5 to 575 µmol in patients without cardiac damage. Higher levels also correlate with disease progression: patients whose disease worsened had median levels between 791 and 2,247 µmol per 24 hours. Each meaningful increase in serotonin markers raised the odds of death by about 7%.
A blood test called NT-proBNP, which reflects how much strain the heart is under, is also used for ongoing monitoring.
Screening and Monitoring Schedule
The European Neuroendocrine Tumor Society recommends that all patients with carcinoid syndrome receive a baseline echocardiogram, followed by repeat studies every 6 to 12 months. NT-proBNP and 5-HIAA levels should be checked on the same schedule. This is important because carcinoid heart disease can progress rapidly, and catching worsening valve function early opens the door to timely surgical intervention.
Medical Treatment
The foundation of medical treatment is controlling the hormones that drive valve damage. Somatostatin analogs, given as monthly injections, reduce serotonin release from the tumors and help manage flushing and diarrhea. While they don’t reverse existing valve damage, they may slow progression by lowering the hormone burden the heart is exposed to.
A newer oral medication that blocks serotonin production at an earlier step in the pathway has shown promise as an addition to somatostatin analogs. Early evidence suggests this combination may help prevent further valve fibrosis, though its long-term effect on heart disease progression is still being studied. Diuretics and other standard heart failure medications can help manage fluid overload symptoms, but they address the consequences of valve damage rather than the cause.
When Valve Replacement Surgery Is Needed
Surgery becomes the primary option when right-sided heart failure is progressing and echocardiography shows moderate to severe valve regurgitation. The tricuspid valve is always involved in surgical candidates and is usually severely leaky. The pulmonary valve typically shows a mix of stenosis and regurgitation. Both valves are often replaced in the same operation.
The decision to operate requires a multidisciplinary team weighing cardiac function against the patient’s overall cancer status. Timing matters: studies consistently show that earlier intervention produces better outcomes than waiting until heart failure is advanced. Before surgery, doctors optimize nutritional status and ensure hormone levels are controlled with somatostatin analogs, reducing the risk of a dangerous complication called carcinoid crisis during the procedure.
Early postoperative survival is approximately 90%. At one year after surgery, survival is about 71%, and at five years it drops to roughly 43%. These numbers reflect the reality that patients are also living with metastatic cancer, so survival depends on both the heart disease and the underlying tumor biology. Still, for patients with severe valve dysfunction, surgery provides meaningful symptom relief and improved quality of life that medical therapy alone cannot achieve.
Long-Term Outlook
Carcinoid heart disease significantly reduces survival compared to carcinoid syndrome without cardiac involvement. Higher serotonin byproduct levels predict worse outcomes, reinforcing how important it is to control hormone production aggressively. Even after successful valve replacement, lifelong monitoring with echocardiograms and blood markers every 6 to 12 months is necessary because new plaque can form on replacement valves or in other areas of the heart. The disease can progress quickly and unpredictably, making consistent follow-up the single most important factor in catching changes before they become irreversible.