What is ICD-10 code I50.21?

I50.21 is the ICD-10-CM diagnosis code for Acute systolic (congestive) heart failure. A sudden worsening of heart function where the heart's left chamber cannot pump blood effectively to the body, causing fluid buildup in the lungs and tissues. I50.21 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. I50.21 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. I50.21 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. I50.21 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does I50.21 map to under V28?

I50.21 maps to CMS-HCC V28 225 (Acute Heart Failure (Excludes Acute on Chronic)). The category number and label come from the CMS-HCC V28 model file for payment year 2026.

What does I50.21 pay in RAF?

I50.21 carries a community, non-dual, aged (CNA) RAF weight of 0.360 under CMS-HCC V28 for payment year 2026. The weight comes from the CMS V28 relative-factor file, not a hand-typed table.

What is the V28 vs V24 difference for I50.21?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For I50.21, V28 maps to Acute Heart Failure (Excludes Acute on Chronic) at RAF 0.360 while V24 mapped to Congestive Heart Failure at RAF 0.331. Both models can still appear in legacy data and in payer-specific lookback periods.

What documentation supports I50.21?

Documentation must establish acute systolic heart failure, a current exacerbation, new-onset symptoms, or an ED/inpatient narrative describing acute decompensation with reduced EF. Do not report I50.21 at a routine follow-up visit for a patient whose acute episode has resolved. The correct follow-up code is I50.22 (chronic systolic HF) unless the chart supports a new acute event. V28 HCC 225 (Acute Heart Failure, Excludes Acute on Chronic) at RAF 0.36. Acute systolic HF maps to the acute-HF HCC, a distinct category from the chronic-HF HCC 226, even though the community coefficient is the same. Because I50.21 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. MEAT is generic documentation evidence, not a payer-specific rule.

2026 ICD-10-CM I50.21: Acute systolic (congestive)

I50.21 maps to CMS-HCC V28 225 (RAF 0.360). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC coding software

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Code lookupI50.21Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the circulatory system (I00-I99) / Other forms of heart disease (I30-I5A)

I50.21

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Acute systolic (congestive) heart failure

A sudden worsening of heart function where the heart's left chamber cannot pump blood effectively to the body, causing fluid buildup in the lungs and tissues.

Buddy Insight

Acute systolic congestive heart failure represents a sudden onset or rapid worsening of systolic dysfunction requiring urgent medical intervention.

CMS-HCC V28

Mapped

HCC 225

Acute Heart Failure (Excludes...

RAF 0.360

CMS-HCC V24

Mapped

HCC 85

Congestive Heart Failure

RAF 0.331

ACA/HHS

Mapped

HCC 130

HHS-HCC 130

Varies by metal level

ESRD/PACE

Mapped

HCC 85

Congestive Heart Failure

RAF 0.063

RXHCC

Mapped

HCC 186

Heart Failure

RAF 0.110

Code Book Path

Official

I50Heart failure

I50.2Systolic (congestive) heart failure

I50.21Acute systolic (congestive) heart failure

Inclusion Terms

Official

Heart failure with reduced ejection fraction [HFrEF]
Systolic left ventricular heart failure

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for I50.21 in this effective period.

Related Child Codes

Official

I50.20Unspecified systolic (congestive) heart failure

I50.22Chronic systolic (congestive) heart failure

I50.23Acute on chronic systolic (congestive) heart failure

Includes

Official

ICD-10-CM does not list Includes notes for I50.21 in this effective period.

Excludes 1

Official

combined systolic (congestive) and diastolic (congestive) heart failure (I50.4-)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for I50.21 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for I50.21 in this effective period.

Code Also

Official

end stage heart failure, if applicable (I50.84)

Buddy Documentation Tip

HCC Buddy guidance

Provider must explicitly document 'acute' systolic heart failure or acute decompensation of systolic function

Clinical indicators of acuity: acute pulmonary edema, new onset dyspnea, rapid weight gain, hypoxia

Ejection fraction demonstrating reduced systolic function

Precipitating factors such as medication noncompliance, dietary indiscretion, ischemia, or arrhythmia

MEAT Support

HCC Buddy guidance

Provider must explicitly document 'acute' systolic heart failure or acute decompensation of systolic function

Clinical indicators of acuity: acute pulmonary edema, new onset dyspnea, rapid weight gain, hypoxia

Ejection fraction demonstrating reduced systolic function

Precipitating factors such as medication noncompliance, dietary indiscretion, ischemia, or arrhythmia

Audit Caution

HCC Buddy guidance

Coding acute systolic heart failure when documentation actually supports acute on chronic (I50.23) — most acute episodes occur in patients with known chronic heart failure

Using this code for outpatient stable visits when the acute episode has resolved

Assuming all emergency department heart failure presentations are 'acute' without provider documentation

Not recognizing that acute heart failure typically resolves to a chronic state requiring code change on follow-up

Common Mistakes

HCC Buddy guidance

I50.23 — Acute on chronic systolic heart failure: use when the patient has pre-existing chronic heart failure with acute worsening

I50.22 — Chronic systolic heart failure: use when the condition is long-standing without acute exacerbation

I50.20 — Unspecified systolic heart failure: less specific, does not indicate acuity

I50.31 — Acute diastolic heart failure: diastolic involves impaired relaxation with preserved ejection fraction

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is I50.21 an HCC code?

Yes. I50.21 (Acute systolic (congestive) heart failure) maps to Acute Heart Failure (Excludes Acute on Chronic) under the CMS-HCC V28 risk adjustment model (and Congestive Heart Failure under V24), with a community non-dual aged RAF of 0.360. It is billable for payment year 2026.

Coder answer: I50.21 is billable and maps to V28 HCC 225, Acute Heart Failure (Excludes Acute on Chronic). Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: I50.21
Description: Acute systolic (congestive) heart failure
HCC (V28): HCC 225 — Acute Heart Failure (Excludes Acute on Chronic)
RAF: 0.360
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 225, Acute Heart Failure (Excludes Acute on Chronic)

0.360

V24HCC 85, Congestive Heart Failure

0.331

ESRDHCC 85, Congestive Heart Failure

0.063

RxHCCHCC 186, Heart Failure

0.110

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work I50.21 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for I50.21

For I50.21 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed I50.21 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

I50.21 is the ICD-10-CM diagnosis code for acute systolic (congestive) heart failure. A sudden worsening of heart function where the heart's left chamber cannot pump blood effectively to the body, causing fluid buildup in the lungs and tissues. I50.21 sits in the ICD-10-CM chapter for diseases of the circulatory system (i00-i99), within the section covering other forms of heart disease (i30-i5a).

Under the CMS-HCC V28 risk adjustment model, I50.21 maps to Acute Heart Failure (Excludes Acute on Chronic) (HCC 225) with a community, non-dual, aged base RAF weight of 0.360. Under the older CMS-HCC V24 model, I50.21 maps to Congestive Heart Failure (HCC 85) with a community, non-dual, aged base RAF weight of 0.331. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Documentation must establish acute systolic heart failure, a current exacerbation, new-onset symptoms, or an ED/inpatient narrative describing acute decompensation with reduced EF. Because I50.21 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for I50.21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Documentation must establish acute systolic heart failure, a current exacerbation, new-onset symptoms, or an ED/inpatient narrative describing acute decompensation with reduced EF.
•Do not report I50.21 at a routine follow-up visit for a patient whose acute episode has resolved. The correct follow-up code is I50.22 (chronic systolic HF) unless the chart supports a new acute event.
•V28 HCC 225 (Acute Heart Failure, Excludes Acute on Chronic) at RAF 0.36. Acute systolic HF maps to the acute-HF HCC, a distinct category from the chronic-HF HCC 226, even though the community coefficient is the same.

Clinical Significance

Acute systolic congestive heart failure represents a sudden onset or rapid worsening of systolic dysfunction requiring urgent medical intervention. These patients typically present with acute pulmonary edema, respiratory distress, and hemodynamic instability. The acute designation indicates higher acuity care needs and often correlates with hospital admission.

Documentation Requirements

✓Provider must explicitly document 'acute' systolic heart failure or acute decompensation of systolic function
✓Clinical indicators of acuity: acute pulmonary edema, new onset dyspnea, rapid weight gain, hypoxia
✓Ejection fraction demonstrating reduced systolic function
✓Precipitating factors such as medication noncompliance, dietary indiscretion, ischemia, or arrhythmia
✓Treatment response including intravenous diuretics, vasodilators, or inotropic support
✓Distinction from acute on chronic — this code implies no pre-existing chronic heart failure

Commonly Confused Codes

•I50.23: Acute on chronic systolic heart failure: use when the patient has pre-existing chronic heart failure with acute worsening
•I50.22: Chronic systolic heart failure: use when the condition is long-standing without acute exacerbation
•I50.20: Unspecified systolic heart failure: less specific, does not indicate acuity
•I50.31: Acute diastolic heart failure: diastolic involves impaired relaxation with preserved ejection fraction
•J81.0: Acute pulmonary edema: a manifestation of heart failure, not a substitute for the heart failure code