ICD-10-CM Code I33.9

Acute and subacute endocarditis, unspecified

Version 2021 Billable Code

Valid for Submission

I33.9 is a billable code used to specify a medical diagnosis of acute and subacute endocarditis, unspecified. The code is valid for the fiscal year 2021 for the submission of HIPAA-covered transactions. The ICD-10-CM code I33.9 might also be used to specify conditions or terms like abscess at site of interatrial communication, abscess at site of ventricular septal defect, abscess of cardiac septum, abscess of cardiac septum, acute and subacute endocarditis, acute endocarditis, etc

Short Description:Acute and subacute endocarditis, unspecified
Long Description:Acute and subacute endocarditis, unspecified

Tabular List of Diseases and Injuries

The Tabular List of Diseases and Injuries is a list of ICD-10 codes, organized "head to toe" into chapters and sections with guidance for inclusions, exclusions, descriptions and more. The following references are applicable to the code I33.9:

Inclusion Terms

Inclusion Terms
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
  • Acute endocarditis NOS
  • Acute myoendocarditis NOS
  • Acute periendocarditis NOS
  • Subacute endocarditis NOS
  • Subacute myoendocarditis NOS
  • Subacute periendocarditis NOS

Index to Diseases and Injuries

The Index to Diseases and Injuries is an alphabetical listing of medical terms, with each term mapped to one or more ICD-10 code(s). The following references for the code I33.9 are found in the index:


The following clinical terms are approximate synonyms or lay terms that might be used to identify the correct diagnosis code:

  • Abscess at site of interatrial communication
  • Abscess at site of ventricular septal defect
  • Abscess of cardiac septum
  • Abscess of cardiac septum
  • Acute and subacute endocarditis
  • Acute endocarditis
  • Acute endocarditis co-occurrent with human immunodeficiency virus infection
  • Acute myoendocarditis
  • Acute nonbacterial endocarditis
  • Acute periendocarditis
  • Heart disease co-occurrent with human immunodeficiency virus infection
  • Subacute endocarditis
  • Subacute myoendocarditis
  • Subacute pericarditis
  • Subacute periendocarditis

Diagnostic Related Groups

The ICD-10 code I33.9 is grouped in the following groups for version MS-DRG V38.0 What are Diagnostic Related Groups?
The Diagnostic Related Groups (DRGs) are a patient classification scheme which provides a means of relating the type of patients a hospital treats. The DRGs divides all possible principal diagnoses into mutually exclusive principal diagnosis areas referred to as Major Diagnostic Categories (MDC).
applicable from 10/01/2020 through 09/30/2021.


Convert I33.9 to ICD-9

  • 421.9 - Ac/subac endocardit NOS

Code Classification

  • Diseases of the circulatory system (I00–I99)
    • Other forms of heart disease (I30-I52)
      • Acute and subacute endocarditis (I33)

Code History

  • FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016
    (First year ICD-10-CM implemented into the HIPAA code set)
  • FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
  • FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
  • FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
  • FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020
  • FY 2021 - No Change, effective from 10/1/2020 through 9/30/2021

Information for Patients


Endocarditis, also called infective endocarditis (IE), is an inflammation of the inner lining of the heart. The most common type, bacterial endocarditis, occurs when germs enter your heart. These germs come through your bloodstream from another part of your body, often your mouth. Bacterial endocarditis can damage your heart valves. If untreated, it can be life-threatening. It is rare in healthy hearts.

Risk factors include having

  • An abnormal or damaged heart valve
  • An artificial heart valve
  • Congenital heart defects

The signs and symptoms of IE can vary from person to person. They also can vary over time in the same person. Symptoms you might notice include fever, shortness of breath, fluid buildup in your arms or legs, tiny red spots on your skin, and weight loss. Your doctor will diagnose IE based on your risk factors, medical history, signs and symptoms, and lab and heart tests.

Early treatment can help you avoid complications. Treatment usually involves high-dose antibiotics. If your heart valve is damaged, you may need surgery.

If you're at risk for IE, brush and floss your teeth regularly, and have regular dental checkups. Germs from a gum infection can enter your bloodstream. If you are at high risk, your doctor might prescribe antibiotics before dental work and certain types of surgery.

NIH: National Heart, Lung, and Blood Institute

  • Culture-negative endocarditis (Medical Encyclopedia)
  • Endocarditis (Medical Encyclopedia)
  • Endocarditis - children (Medical Encyclopedia)

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