I33.9 Acute and subacute endocarditis, unspecified

Billable ICD-10-CM code, FY2026. Acts as a Major Complication or Comorbidity (MCC) as a secondary diagnosis.

Applicable to

• Acute endocarditis NOS
• Acute myoendocarditis NOS
• Acute periendocarditis NOS
• Subacute endocarditis NOS
• Subacute myoendocarditis NOS
• Subacute periendocarditis NOS

Applies from I33 Acute and subacute endocarditis

Excludes1 (never code together)

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

MS-DRG index

Defines the logic of DRG(s) 288-290 in MDC 05.

Approximate ICD-9-CM (GEMs)

• 421.9 Acute endocarditis, unspecified

Diagnosis Index entries for I33.9

• Endocarditis (chronic) (marantic) (nonbacterial) (thrombotic) (valvular) › acute or subacute
• Endocarditis (chronic) (marantic) (nonbacterial) (thrombotic) (valvular) › aortic (heart) (nonrheumatic) (valve) › acute or subacute
• Endocarditis (chronic) (marantic) (nonbacterial) (thrombotic) (valvular) › mitral (chronic) (double) (fibroid) (heart) (inactive) (valve) (with chorea) › nonrheumatic › acute or subacute
• Endocarditis (chronic) (marantic) (nonbacterial) (thrombotic) (valvular) › pulmonary (chronic) (heart) (valve) › acute or subacute
• Endocarditis (chronic) (marantic) (nonbacterial) (thrombotic) (valvular) › toxic
• Endocarditis (chronic) (marantic) (nonbacterial) (thrombotic) (valvular) › tricuspid (chronic) (heart) (inactive) (rheumatic) (valve) (with chorea) › nonrheumatic › acute or subacute

Nearby codes

• I33 Acute and subacute endocarditis
• I33.0 Acute and subacute infective endocarditis
• I33.9 Acute and subacute endocarditis, unspecified (this code)