Infective endocarditis is a serious infection of the inner lining of the heart, almost always involving one or more heart valves. Bacteria (or, rarely, fungi) settle on damaged valve tissue and form clumps called vegetations, clusters of microorganisms, blood cells, and clotting proteins that can destroy valve structures and send infected debris throughout the body. In-hospital mortality ranges from 15% to 30%, making it one of the most dangerous cardiac infections.
How the Infection Takes Hold
A healthy heart lining is naturally resistant to infection. For endocarditis to develop, two things need to happen: the valve surface has to be damaged first, and then bacteria have to enter the bloodstream.
Valve damage can come from turbulent blood flow around an already abnormal valve, from the mechanical trauma of a catheter or pacemaker wire, or from tiny particles injected alongside drugs in intravenous drug use. Once the surface is disrupted, platelets and clotting proteins pile up to form a small, sterile clot on the valve. This clot becomes the landing pad for bacteria. When bacteria circulate through the blood and stick to it, they trigger even more platelet buildup, which in turn attracts more bacteria. The growing mass, now called a vegetation, shields the microorganisms from the immune system and allows the infection to expand largely unchecked.
Who Is Most at Risk
People with pre-existing valve problems face the highest risk. This includes anyone with a prosthetic (replacement) heart valve, a history of previous endocarditis, congenital heart disease, or significant valve regurgitation or stenosis. Having heart valve surgery of any kind increases susceptibility. People who inject drugs are also at elevated risk because repeated injections both introduce bacteria into the bloodstream and damage heart valves through particulate matter carried in the injection.
Implanted cardiac devices, such as pacemakers and defibrillators with leads that pass through the heart, create additional surfaces where bacteria can attach. Even hypertrophic obstructive cardiomyopathy, a condition that thickens part of the heart muscle and disrupts blood flow, is now recognized as a predisposing factor.
Symptoms and Physical Signs
Endocarditis often starts with nonspecific symptoms: fever above 38°C (100.4°F), fatigue, loss of appetite, and night sweats. Because these overlap with many common illnesses, the infection is frequently missed early on. A new or changing heart murmur, caused by the vegetation interfering with valve function, is one of the more telling signs.
There are four classic skin and eye findings associated with the disease, though none are especially common. Splinter hemorrhages, tiny vertical blood streaks under the fingernails, appear in roughly 39% of cases. Osler nodes are painful red bumps on the pads of the fingers or toes, seen in about 7% of patients, thought to result from immune complexes depositing in small blood vessels. Janeway lesions are painless red or purple flat spots on the palms and soles, occurring in around 2% of cases. Roth spots, white-centered hemorrhages visible on an eye exam, show up about 3% of the time. When any of these appear alongside a fever, they strongly suggest endocarditis.
How It Is Diagnosed
Doctors use a standardized checklist called the Duke criteria, most recently updated in 2023, to determine how likely a diagnosis of endocarditis is. The system divides evidence into major and minor criteria.
The major criteria center on three pillars. First, blood cultures: finding typical bacteria in two or more separate blood draws is a major criterion. Second, imaging: an echocardiogram (ultrasound of the heart) or cardiac CT showing a vegetation, a hole in a valve leaflet, an abscess, or significant new valve leakage counts as major evidence. Specialized PET/CT scans can also detect abnormal metabolic activity around prosthetic valves or implanted devices. Third, if a surgeon directly sees signs of infection during heart surgery, that observation qualifies as a major criterion on its own.
Minor criteria include a predisposing heart condition or injection drug use, fever, vascular events like emboli or mycotic aneurysms, immunologic phenomena like Osler nodes or Roth spots, and blood cultures that are suggestive but don’t fully meet the major threshold. A definite diagnosis requires meeting either two major criteria, one major plus three minor, or five minor criteria.
Complications From Infected Debris
The vegetations on an infected valve are fragile. Pieces can break off and travel through the bloodstream, lodging in distant organs. The brain and spleen are the two most frequently affected.
Stroke is the most feared complication, occurring in 20% to 40% of left-sided endocarditis cases. When researchers performed brain MRIs on patients with left-sided endocarditis who had no neurological symptoms, over 70% already showed evidence of small embolic events they hadn’t felt. Embolic strokes in endocarditis are also more prone to bleeding into the damaged brain tissue afterward, a complication called hemorrhagic transformation. In patients with prosthetic valve endocarditis, this hemorrhagic conversion rate reaches 42%.
Splenic infarctions are similarly common but often silent. One study using contrast ultrasound found that 61% of asymptomatic left-sided endocarditis patients had spleen infarctions within 10 days of diagnosis. Mycotic aneurysms, weakened bulges in artery walls caused by infected emboli, develop in 2% to 4% of patients when checked clinically, but closer to 9% when cerebral angiography is performed regardless of symptoms. Most occur in branches of the middle cerebral artery. If one ruptures, the resulting brain hemorrhage carries a mortality rate of 35% to 40%.
Antibiotic Treatment
Endocarditis requires prolonged intravenous antibiotic therapy, typically lasting 2 to 6 weeks depending on the type of bacteria involved and whether the infection is on a natural or prosthetic valve. The antibiotics need to be bactericidal, meaning they kill bacteria outright rather than simply slowing their growth, because the immune system has limited access to organisms buried inside vegetations.
Treatment usually involves a combination of two antibiotics working together to penetrate the vegetation and overcome bacterial defenses. The specific drugs chosen depend on what grows in blood cultures. For infections caused by the most common culprit, Staphylococcus aureus, the antibiotic regimen hinges on whether the strain is resistant to standard antibiotics. Drug-resistant strains require different agents than drug-sensitive ones. Prosthetic valve infections generally need longer courses and additional antibiotics compared to infections on natural valves.
When Surgery Becomes Necessary
Not every case of endocarditis can be cured with antibiotics alone. Surgery to repair or replace the infected valve is considered when the infection causes heart failure from severe valve damage, when fever and positive blood cultures persist longer than 5 to 7 days despite appropriate antibiotics, or when large vegetations threaten to send more emboli to the brain or other organs.
For left-sided endocarditis, guidelines recommend urgent or emergency surgery when vegetations exceed 10 mm and there is already evidence of embolic events despite antibiotic therapy. Fungal infections and highly resistant organisms are also strong triggers for surgical intervention because antibiotics alone rarely eradicate them. Right-sided endocarditis, which most commonly affects people who inject drugs, has a somewhat higher threshold for surgery. On the right side, the vegetation generally needs to exceed 20 mm with ongoing infection or septic blood clots traveling to the lungs before surgery is indicated.
Long-Term Outlook
Surviving the initial hospitalization is the steepest hurdle. With in-hospital mortality between 15% and 30%, the acute phase is genuinely dangerous. For those who make it through treatment, survival rates are 80% to 90% at one year, 70% to 80% at two years, and 60% to 70% at five years. The decline over time reflects both the lasting heart damage from the infection and the ongoing risk in people whose underlying conditions made them vulnerable in the first place.
Preventing Endocarditis
The American Heart Association recommends preventive antibiotics before certain dental procedures for people at highest risk. This includes anyone with a prosthetic heart valve, a history of previous endocarditis, certain types of congenital heart disease, or a heart transplant with valve problems. The dental procedures that warrant prophylaxis are extractions, oral surgery, scaling (deep cleaning), and root canal treatment, all situations where bacteria from the mouth can enter the bloodstream in significant numbers.
For nondental procedures, such as colonoscopies or urinary tract procedures, there are currently no formal recommendations for preventive antibiotics due to insufficient evidence. Good dental hygiene, including regular brushing, flossing, and dental checkups, is considered just as important as prophylactic antibiotics for reducing the overall risk of mouth bacteria seeding the bloodstream.