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Chapter 9: Diseases of the circulatory system (I00–I99)

Heart and blood-vessel disease: high blood pressure, coronary artery disease and heart attack, heart failure, abnormal heart rhythms, valve disorders, deep vein thrombosis and varicose veins.

Chapter 9 spans codes I00–I99 in the FY2027 ICD-10-CM tabular list. This guide explains 60 of its most common codes — select a code for its official description, a plain-English explanation and a note on when the code is used.

ICD-10 Chapter 9: Circulatory System — illustrative image

Codes in this chapter

CodeOfficial descriptionIn plain words
I10Essential (primary) hypertensionEssential (primary) hypertension is persistently raised blood pressure with no single identifiable cause, the commonest form.
I11.0Hypertensive heart disease with heart failureHypertensive heart disease with heart failure: long-standing high blood pressure has damaged the heart so it cannot pump effectively.
I11.9Hypertensive heart disease without heart failureHypertensive heart disease without heart failure: heart changes caused by long-standing high blood pressure.
I12.0Hypertensive chronic kidney disease with stage 5 chronic kidney disease or end stage renal diseaseKidney damage caused by long-standing high blood pressure, advanced to stage 5 chronic kidney disease or kidney failure.
I12.9Hypertensive chronic kidney disease with stage 1 through stage 4 chronic kidney disease, or unspecified chronic kidney diseaseKidney damage caused by long-standing high blood pressure, with chronic kidney disease stage 1 to 4.
I13.0Hypertensive heart and chronic kidney disease with heart failure and stage 1 through stage 4 chronic kidney disease, or unspecified chronic kidney diseaseCombined heart and kidney disease caused by hypertension, with heart failure and stage 1–4 chronic kidney disease.
I13.10Hypertensive heart and chronic kidney disease without heart failure, with stage 1 through stage 4 chronic kidney disease, or unspecified chronic kidney diseaseCombined heart and kidney disease caused by hypertension, without heart failure, with stage 1–4 chronic kidney disease.
I13.2Hypertensive heart and chronic kidney disease with heart failure and with stage 5 chronic kidney disease, or end stage renal diseaseCombined heart and kidney disease caused by hypertension, with heart failure and stage 5 CKD or kidney failure.
I16.0Hypertensive urgencyHypertensive urgency is a severe rise in blood pressure without signs of acute organ damage.
I16.1Hypertensive emergencyHypertensive emergency is a severe rise in blood pressure that is damaging organs such as the brain, heart or kidneys.
I20.9Angina pectoris, unspecifiedAngina pectoris is chest pain or tightness caused by reduced blood flow to the heart muscle, usually with exertion.
I21.3ST elevation (STEMI) myocardial infarction of unspecified siteAn ST-elevation myocardial infarction (STEMI) is a heart attack in which a coronary artery is completely blocked.
I21.4Non-ST elevation (NSTEMI) myocardial infarctionA non-ST-elevation myocardial infarction (NSTEMI) is a heart attack in which a coronary artery is partially blocked.
I24.9Acute ischemic heart disease, unspecifiedAcute ischaemic heart disease: a sudden reduction in blood flow to the heart muscle, recorded without further detail.
I25.10Atherosclerotic heart disease of native coronary artery without angina pectorisAtherosclerotic heart disease: the coronary arteries are narrowed by fatty plaques, here without angina symptoms.
I25.110Atherosclerotic heart disease of native coronary artery with unstable angina pectorisCoronary artery disease with unstable angina: chest pain occurring at rest or worsening, signalling an unstable plaque.
I25.119Atherosclerotic heart disease of native coronary artery with unspecified angina pectorisCoronary artery disease with angina: narrowed coronary arteries cause exertional chest pain.
I25.2Old myocardial infarctionAn old myocardial infarction is a previous heart attack, healed, found on a heart tracing or history.
I25.5Ischemic cardiomyopathyIschaemic cardiomyopathy is weakening of the heart muscle caused by coronary artery disease and previous heart damage.
I26.99Other pulmonary embolism without acute cor pulmonaleA pulmonary embolism is a blood clot that travels to the lungs and blocks a pulmonary artery; this code covers other forms without acute heart strain.
I27.20Pulmonary hypertension, unspecifiedPulmonary hypertension is raised blood pressure in the arteries of the lungs, straining the right side of the heart.
I30.9Acute pericarditis, unspecifiedAcute pericarditis is sudden inflammation of the pericardium, the sac around the heart, causing sharp chest pain.
I31.39Other pericardial effusion (noninflammatory)A pericardial effusion is a build-up of fluid in the sac around the heart that is not due to inflammation.
I34.0Nonrheumatic mitral (valve) insufficiencyMitral insufficiency is leakage of the mitral valve, letting blood flow backwards into the left atrium; here not rheumatic in origin.
I35.0Nonrheumatic aortic (valve) stenosisAortic stenosis is narrowing of the aortic valve, obstructing blood flow out of the heart; here not rheumatic in origin.
I35.1Nonrheumatic aortic (valve) insufficiencyAortic insufficiency is leakage of the aortic valve, letting blood flow back into the heart; here not rheumatic in origin.
I42.9Cardiomyopathy, unspecifiedCardiomyopathy is a disease of the heart muscle that makes it harder to pump blood; type not specified here.
I44.7Left bundle-branch block, unspecifiedLeft bundle-branch block is a delay or block in the electrical pathway of the heart's left side, seen on an ECG.
I47.10Supraventricular tachycardia, unspecifiedSupraventricular tachycardia (SVT) is a fast heart rhythm starting above the ventricles, causing palpitations.
I47.20Ventricular tachycardia, unspecifiedVentricular tachycardia is a fast, potentially dangerous heart rhythm starting in the ventricles.
I48.0Paroxysmal atrial fibrillationParoxysmal atrial fibrillation is an irregular, often fast heartbeat that starts and stops on its own within days.
I48.19Other persistent atrial fibrillationPersistent atrial fibrillation is a continuous irregular heartbeat lasting more than seven days or needing treatment to stop it.
I48.20Chronic atrial fibrillation, unspecifiedChronic atrial fibrillation is a long-standing irregular heartbeat; 'chronic' here is unspecified as to permanent status.
I48.91Unspecified atrial fibrillationAtrial fibrillation is an irregular and often rapid heart rhythm arising from the upper chambers of the heart.
I48.92Unspecified atrial flutterAtrial flutter is a fast, regular abnormal heart rhythm arising from the upper chambers of the heart.
I49.3Ventricular premature depolarizationVentricular premature depolarisations are extra heartbeats starting in the ventricles, felt as skipped or thumping beats.
I49.9Cardiac arrhythmia, unspecifiedA cardiac arrhythmia is any abnormality of the heart's rhythm; the type is not specified here.
I50.22Chronic systolic (congestive) heart failureChronic systolic heart failure: a long-term weakness of the heart's pumping (contraction) function.
I50.23Acute on chronic systolic (congestive) heart failureAcute on chronic systolic heart failure: a sudden worsening of long-term pumping weakness of the heart.
I50.30Unspecified diastolic (congestive) heart failureDiastolic heart failure: the heart pumps normally but relaxes and fills stiffly, raising pressures; type of course not specified.
I50.32Chronic diastolic (congestive) heart failureChronic diastolic heart failure: long-term stiff filling of the heart with preserved pumping strength.
I50.33Acute on chronic diastolic (congestive) heart failureAcute on chronic diastolic heart failure: a sudden worsening of long-term stiff-filling heart failure.
I50.810Right heart failure, unspecifiedRight heart failure is failure of the right side of the heart, causing fluid to back up into the body and legs.
I50.9Heart failure, unspecifiedHeart failure means the heart cannot pump blood well enough to meet the body's needs, causing breathlessness and fluid build-up.
I51.7CardiomegalyCardiomegaly is an enlarged heart seen on imaging, which can occur with hypertension, valve disease or cardiomyopathy.
I63.9Cerebral infarction, unspecifiedA cerebral infarction is a stroke caused by a blocked artery cutting off blood flow to part of the brain.
I65.23Occlusion and stenosis of bilateral carotid arteriesNarrowing (stenosis) of both carotid arteries in the neck, usually from atherosclerosis, reducing blood flow to the brain.
I69.320Aphasia following cerebral infarctionAphasia (difficulty speaking or understanding language) remaining after a stroke caused by cerebral infarction.
I69.351Hemiplegia and hemiparesis following cerebral infarction affecting right dominant sideWeakness or paralysis of one side of the body (hemiplegia) remaining after a stroke, here on the right dominant side.
I70.0Atherosclerosis of aortaAtherosclerosis of the aorta: fatty plaque build-up in the body's main artery.
I71.40Abdominal aortic aneurysm, without rupture, unspecifiedAn abdominal aortic aneurysm is a widening of the aorta in the abdomen; this code is for one that has not ruptured.
I73.9Peripheral vascular disease, unspecifiedPeripheral vascular disease is narrowing of arteries outside the heart and brain, most often in the legs.
I80.9Phlebitis and thrombophlebitis of unspecified sitePhlebitis and thrombophlebitis mean inflammation of a vein, usually with a clot; the site is not specified here.
I82.409Acute embolism and thrombosis of unspecified deep veins of unspecified lower extremityAcute deep vein thrombosis (DVT): a fresh blood clot in a deep vein of the leg, with vein and side not specified.
I82.90Acute embolism and thrombosis of unspecified veinAn acute blood clot blocking a vein whose name is not specified in the record.
I83.90Asymptomatic varicose veins of unspecified lower extremityVaricose veins are swollen, twisted veins just under the skin of the leg, here without symptoms being recorded.
I87.2Venous insufficiency (chronic) (peripheral)Chronic venous insufficiency means the leg veins do not return blood efficiently, causing aching, swelling and skin changes.
I89.0Lymphedema, not elsewhere classifiedLymphoedema is swelling caused by a build-up of lymph fluid when the lymphatic system cannot drain properly.
I95.1Orthostatic hypotensionOrthostatic hypotension is a fall in blood pressure on standing up, causing light-headedness or fainting.
I95.9Hypotension, unspecifiedHypotension is abnormally low blood pressure; the cause is not specified here.

This guide explains ICD-10-CM codes in plain language for patients, students and other readers. It is educational information only — not coding, billing or medical advice. The code recorded for any real encounter is assigned from the full clinical documentation by the treating team and qualified coders, and only they can decide which code fits a specific case.

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