ICD-10-CM 2027 diagnosis code

I33Acute and subacute endocarditis

Not billable — use a more specific code

I33 is a header code, so it can't be reported by itself. Choose one of the 2 more specific codes beneath it.

Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About I33

I33 is the ICD-10-CM diagnosis code for acute and subacute endocarditis. It belongs to block I30-I5A (other forms of heart disease) and chapter 9 (diseases of the circulatory system). It is a header code, so it can't be reported by itself; one of its 2 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: I33.0 (endocarditis) and I33.9 (unspecified).

Don't report I33 together with the conditions in its Excludes1 note: acute rheumatic endocarditis (I01.1) and endocarditis NOS (I38).

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Specific codes under I33

Coding notes

Excludes1Not coded here — never report together with this code

acute rheumatic endocarditis (I01.1)
endocarditis NOS (I38)

Notes that apply from higher levels

Instructions written at a parent level also apply to I33.

Broader instructions also apply from Chapter 9: Diseases of the circulatory system.

Code history

2016
2017
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2021
2022
2023
2024
2025
2026
2027

FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
No changes since FY2016.

Common questions about I33

Is I33 billable?: No. I33 is a header code. Report one of its more specific subcodes instead.