Heparin for Heart Conditions

Heparin is a prescription medication approved by the U.S. Food and Drug Administration (FDA) to prevent and treat blood clots in veins, lungs, and arteries, including clot-related complications of atrial fibrillation (AFib). Certain heparin products are also approved to prevent clotting during heart surgery and other medical procedures.

How Heparin Works and How It’s Taken

Heparin is a blood thinner called an anticoagulant. It works with a natural protein in the blood to block clotting proteins, including factor Xa and thrombin. This helps prevent new blood clots from forming and existing clots from getting larger. Heparin does not dissolve clots that have already formed.

Doctors prescribe heparin products for:

Atrial fibrillation — To prevent or treat blood clot complications linked to an irregular heartbeat
Heart surgery — To prevent blood from clotting during heart surgery, including open-heart procedures

Depending on the product, heparin may be given as an injection into a vein, a steady flow of medicine into a vein, or a deep injection under the skin under medical supervision.

Typical Dosing for Heart Conditions

Heparin dosing depends on the condition being treated, the person’s weight, and blood clotting test results.

The prescribing information provides general adult treatment doses that may be used for blood clot complications associated with AFib. These include:

Continuous intravenous (IV) infusion — An initial dose of 5,000 units is injected into a vein. This may be followed by 20,000 to 40,000 units over 24 hours through a steady flow of medicine into a vein.
Intermittent IV injection — An initial dose of 10,000 units is injected into a vein, followed by 5,000 to 10,000 units every four to six hours.
Deep injection under the skin — An initial dose of 5,000 units is injected into a vein, followed by 10,000 to 20,000 units under the skin. After that, a person may receive 8,000 to 10,000 units every eight hours or 15,000 to 20,000 units every 12 hours.

These adult dosing guidelines are based on a person weighing about 68 kilograms. Doctors adjust doses based on blood clotting tests and individual needs.

Heparin may be used to prevent blood clotting during open-heart surgery when a machine circulates blood outside the body.

Initial dose — At least 150 units per kilogram of body weight
Procedures lasting less than 60 minutes — A dose of 300 units per kilogram is frequently used
Procedures lasting longer than 60 minutes — A dose of 400 units per kilogram is frequently used

The healthcare team determines the appropriate dose based on the procedure and the person’s needs.

This information is based on the prescribing information, but your healthcare provider may tailor your treatment plan. Always follow their guidance.

Heparin Side Effects

Heparin can cause side effects, including:

Bleeding or bruising more easily than usual
Thrombocytopenia (low platelet count)
Irritation where the shot is given (such as redness or skin discoloration, mild pain, or swelling)
Higher liver enzyme levels on blood tests (aminotransferase elevations)

Serious Side Effects and Warnings

Heparin can cause serious side effects that may require immediate medical attention. These include:

Hemorrhage — Serious bleeding can happen in many parts of the body.
Heparin-induced thrombocytopenia (HIT) and HIT with thrombosis (HITT) — These immune reaction can lower platelets and can also cause dangerous blood clots, such as deep vein thrombosis (DVT), pulmonary embolism (PE), stroke, or heart attack.
Severe allergic reactions — Hypersensitivity reactions can include anaphylactoid reactions, which can cause trouble breathing, hives, or shock.
Skin necrosis — Skin tissue damage can happen at the injection site or after heparin is given.
Hyperkalemia (high potassium levels) — An increase in potassium in the blood can affect how the heart works.

Get medical help right away if you think you are having a serious reaction.

If you experience serious side effects, you can report them to the FDA online or by calling 1-800-FDA-1088. You can also contact the drug's manufacturer.

What To Know Before Taking Heparin

Before starting heparin, your doctor will check how well your blood clots using tests such as activated partial thromboplastin time (aPTT) and international normalized ratio (INR). Your doctor will also measure your platelet count. Platelets are blood cells that help stop bleeding.

Tell your doctor if you:

Are allergic to heparin or pork products
Have a history of unusual bleeding or low platelet counts

Tell your doctor about all medicines you take, including prescription drugs, over-the-counter medicines, vitamins, and herbal supplements.

Do not receive heparin if you:

Have a history of HIT, a serious reaction that lowers platelet counts and may cause blood clots
Have a known allergy to heparin or pork products
Have active bleeding that cannot be controlled, unless it is caused by disseminated intravascular coagulation (DIC)
Cannot have the required blood clotting tests at regular intervals when receiving full-dose heparin

Some heparin products are also contraindicated in people with severe thrombocytopenia, meaning a very low platelet count.

Heparin is also FDA-approved for other uses, depending on the product, including:

DVT — To prevent or treat blood clots in deep veins
PE — To prevent or treat blood clots in the lungs
Peripheral arterial embolism — To prevent or treat blood clots that block arteries
DIC — To treat a serious condition that causes abnormal blood clotting throughout the body
Blood transfusions and other medical procedures — To prevent clotting when blood is transfused or circulated outside the body, including during dialysis
Intravenous catheter care — To help prevent blood clots from blocking an intravenous catheter

If you are pregnant, planning to become pregnant, or breastfeeding, tell your doctor before receiving heparin. The risks and recommendations may differ depending on the heparin product.

Community FAQs

These answers are fact-checked by our editorial staff.

How effective is heparin for heart conditions?

Heparin is FDA-approved to prevent or treat blood clot complications linked to atrial fibrillation (AFib). It is also used during heart surgery to prevent blood from clotting while a heart-lung machine circulates blood outside the body.

The prescribing information does not provide specific success rates for these uses. Doctors use blood tests to check heparin’s effects and adjust treatment when needed.

How long does heparin take to work for heart conditions?

Heparin starts working immediately when injected into a vein. When injected under the skin, its effects take longer to develop.

How long heparin’s effects last depends on the dose and how it is given.

Does heparin interact with other medicines?

Yes. Heparin can interact with other medicines, including:

Aspirin and pain relievers — Medicines such as aspirin and ibuprofen may increase the risk of bleeding.
Other blood thinners — Medicines such as warfarin may increase bleeding risk when used with heparin.
Certain antibiotics — Medicines such as tetracyclines may reduce heparin’s blood-thinning effects.
Other medicines — Antihistamines and intravenous nitroglycerin may also reduce heparin’s effects.

Tell your doctor about all medicines and supplements you take before starting heparin. Your doctor may adjust your treatment or monitor you more closely to help prevent serious side effects.