Why untreated endocarditis is dangerous

Endocarditis is a serious infection of the inner lining of the heart, most often involving the heart valves. Though rare, it can cause devastating complications if left untreated. When bacteria or fungi enter the bloodstream and settle in the heart, they form clumps of infected material called vegetations. These vegetations damage the heart, spread infection, and send infected clots throughout the body.

Without prompt treatment—typically involving antibiotics and sometimes surgery—endocarditis can rapidly progress and become life-threatening. Understanding its complications can underscore the urgency of early diagnosis and care.

Valve destruction

One of the most severe complications is valve destruction. The heart valves regulate blood flow between the heart chambers and out to the rest of the body. When bacteria attach to a valve, they can erode the tissue, leading to:

  • Valve perforation (holes in the valve)

  • Flail leaflet (loss of valve structure)

  • Valve regurgitation (leaking)

This damage disrupts normal heart function, causing the heart to work harder and become less efficient. Left untreated, valve destruction can lead to irreversible heart failure.

Heart failure

When heart valves are damaged and blood doesn’t flow properly, heart failure can develop. This means the heart can’t pump enough blood to meet the body’s needs.

Symptoms of heart failure include:

  • Shortness of breath, especially when lying down

  • Swelling in the legs, ankles, or abdomen

  • Fatigue and weakness

  • Rapid heartbeat or irregular pulse

  • Fluid retention and weight gain

Heart failure due to endocarditis can come on rapidly, especially in acute cases, and may be fatal without intervention.

Stroke and brain complications

Endocarditis increases the risk of stroke and other neurological issues. Pieces of infected material can break off from the heart valves and travel through the bloodstream to the brain, causing:

  • Ischemic stroke (blocked blood flow to the brain)

  • Hemorrhagic stroke (bleeding in the brain)

  • Brain abscess (pocket of infection in brain tissue)

  • Seizures

  • Confusion or altered mental status

These complications can result in permanent disability or death. Strokes in endocarditis patients are often sudden and severe.

Embolic events

Beyond the brain, vegetations can dislodge and cause emboli elsewhere in the body. These infected clots may lodge in:

  • Lungs (pulmonary embolism, especially in right-sided endocarditis)

  • Kidneys (causing infarction or infection)

  • Spleen (resulting in splenic abscess or rupture)

  • Liver (hepatic infarcts)

  • Extremities (limb ischemia or gangrene)

These embolic events lead to pain, organ dysfunction, or tissue death. If not treated, they can require emergency surgery or result in fatal organ failure.

Kidney damage

Untreated endocarditis often affects the kidneys, both directly and indirectly. Emboli may block blood flow, and immune complexes can settle in the kidneys, triggering inflammation (glomerulonephritis). In some cases, the high bacterial load causes sepsis, impairing kidney function.

Kidney complications may include:

  • Hematuria (blood in urine)

  • Proteinuria (protein in urine)

  • Elevated creatinine levels

  • Acute kidney injury or chronic kidney disease

Renal damage may become permanent and require dialysis in severe cases.

Lung involvement

Especially in IV drug users or patients with right-sided endocarditis, the lungs are frequent targets of emboli. This can lead to:

  • Septic pulmonary emboli (infected blood clots in the lungs)

  • Lung abscesses

  • Pneumonia-like symptoms

  • Pleural effusion (fluid around the lungs)

These complications cause shortness of breath, chest pain, coughing, and sometimes coughing up blood.

Sepsis and septic shock

If the infection spreads beyond the heart, it can result in sepsis—a body-wide response to infection. Sepsis can progress to septic shock, characterized by dangerously low blood pressure and multi-organ failure.

Symptoms include:

  • High fever or low body temperature

  • Rapid heartbeat

  • Difficulty breathing

  • Low blood pressure

  • Confusion or lethargy

  • Cold or mottled skin

Septic shock requires emergency ICU care and has a high mortality rate if not treated immediately.

Perivalvular abscess

As endocarditis progresses, infection can spread into the tissue surrounding the valve, forming a perivalvular abscess. This abscess can erode nearby structures and lead to:

  • Heart block (interruption in the heart’s electrical signals)

  • Fistula formation (abnormal connections between heart chambers)

  • Increased valve leakage

  • Need for emergency surgery

Perivalvular abscesses are difficult to detect without echocardiography and often indicate a need for urgent surgical repair.

Conduction abnormalities

When the infection spreads to the heart’s electrical system, it can cause arrhythmias and conduction abnormalities. One serious consequence is complete heart block, where the signal between the atria and ventricles is lost.

This condition may require:

  • Temporary pacing during infection treatment

  • Permanent pacemaker placement if damage is irreversible

Irregular rhythms also increase the risk of stroke, fainting, and sudden cardiac arrest.

Formation of aneurysms

Infective emboli may damage blood vessel walls, leading to the formation of mycotic aneurysms—weak, bulging areas in arteries. These aneurysms can occur in:

  • Brain arteries

  • Aorta

  • Mesenteric arteries (serving the intestines)

  • Renal arteries

If a mycotic aneurysm ruptures, it can cause life-threatening internal bleeding.

Spleen complications

The spleen often receives emboli during left-sided endocarditis. This can lead to:

  • Splenic infarction (tissue death)

  • Splenic abscess (localized infection)

  • Splenic rupture (rare but fatal emergency)

Symptoms include left upper abdominal pain, fever, and tenderness, especially with deep breathing or movement.

Liver damage

Though less common, emboli or systemic inflammation from untreated endocarditis can impair liver function, causing:

  • Elevated liver enzymes

  • Jaundice

  • Hepatic infarction or abscess

Liver involvement complicates medication metabolism and limits antibiotic choices.

Immune system overload

The infection triggers a strong immune response, sometimes leading to:

  • Immune complex deposition in kidneys and joints

  • Vasculitis (inflammation of blood vessels)

  • Anemia of chronic disease

  • Splinter hemorrhages, Osler’s nodes, Janeway lesions

These manifestations can mimic autoimmune diseases and further delay diagnosis if endocarditis is not suspected.

Death

Ultimately, untreated endocarditis can be fatal. Mortality rates are high when the condition progresses unchecked, especially in:

  • Acute endocarditis caused by virulent organisms like Staphylococcus aureus

  • Prosthetic valve infections

  • Fungal endocarditis

  • Cases involving extensive valve destruction or embolic complications

Death can occur due to heart failure, stroke, sepsis, or multi-organ failure.

Who is at greater risk of complications?

Not all patients face the same risk. Complications are more likely in those who:

  • Delay seeking medical attention

  • Have prosthetic heart valves or cardiac devices

  • Have congenital heart disease

  • Use intravenous drugs

  • Are immunocompromised

  • Are infected with resistant or fungal organisms

Early detection and treatment significantly reduce the risk of severe outcomes.

How fast can complications develop?

In acute endocarditis, complications can develop within days or even hours. In subacute endocarditis, symptoms may progress slowly over weeks to months, but complications still eventually arise if left untreated.

The timing varies depending on:

  • The type of organism

  • The person’s immune status

  • Presence of underlying heart disease

But regardless of speed, once complications begin, they tend to accelerate and compound.

Signs you shouldn’t ignore

Early symptoms that could signal complications include:

  • Fever lasting more than a few days

  • Night sweats

  • Weight loss

  • New or changing heart murmurs

  • Shortness of breath

  • Confusion or stroke symptoms

  • Pain in the chest, abdomen, or limbs

  • Blood in urine

Prompt medical evaluation is critical when these signs are present—especially in individuals with known heart conditions.

Preventing complications

The key to preventing endocarditis complications is early and appropriate treatment. Strategies include:

  • Immediate IV antibiotics after diagnosis

  • Regular echocardiograms to assess progression

  • Timely surgical intervention when necessary

  • Close monitoring of organ function

  • Preventive antibiotics for high-risk individuals before dental or surgical procedures

  • Avoidance of IV drug use

Prevention also includes maintaining good dental hygiene and prompt treatment of any infections elsewhere in the body.

Final thoughts

Endocarditis is not an infection to ignore. What starts as a low-grade fever or fatigue can quickly spiral into a life-threatening emergency. The range of complications—from heart failure and stroke to kidney failure and death—underscores the importance of early diagnosis and treatment.

If you or someone you love has risk factors for endocarditis, don’t wait for symptoms to worsen. Recognizing the danger of untreated endocarditis can save lives.