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Many people with congenital heart defects need to take anticoagulants (*blood thinners). Common reasons for this type of treatment include heart valve replacements, heart rhythm disorders or prior complicated surgeries such as a Fontan operation. Blood-thinning medicines slow blood clotting, preventing complications like blood clots forming on artificial valves, valve obstruction and blood clots traveling to the brain and causing stroke.

Anticoagulants are usually given by mouth. In some cases they're given by vein (intravenously) or by injecting them just under the skin (subcutaneously).

Bleeding may be a complication of taking these medications. Tell your health care professional if you begin to bruise easily, or if you notice unusual bleeding anywhere, including bleeding gums or nosebleeds.

Oral medications

Anticoagulants taken by mouth mainly include aspirin, clopidogrel and warfarin These medications decrease clotting tendency by interfering with platelets or blocking the body's production of clotting substances. Your cardiologist will decide which one is right for you.

All drugs may cause adverse effects. Aspirin may upset your stomach. It also may affect platelet function and bleeding times. It may need to be discontinued prior to surgery.

Clopidogrel doesn't require regular blood test monitoring, but it affects platelet function and bleeding times for up to 10 days. So you’ll need to discontinue use before surgery.

Warfarin increases your risk of serious bleeding problems, even when the dose is at the recommended level. Carefully and regularly monitoring the level of blood thinning by testing is required while on warfarin. A value called the INR, or international normalized ratio, tests how quickly your blood clots. Your warfarin dosage will be carefully adjusted to maintain an INR appropriate for your heart condition. You must take your medicine exactly as prescribed. Discuss warfarin use with your health care professional if you are pregnant or planning pregnancy as it may be harmful to your fetus.

Consult with your dentist and health care team on preparation for dental procedures and surgeries. You may need to change your medicines or avoid elective dental work and surgery while taking anticoagulants due to risks of bleeding.

Intravenous medications

Intravenous heparin acts rapidly to thin the blood. When it's stopped, the effect also wears off rapidly. Oral anticoagulants are longer-acting, so if you need elective surgery (including dental surgery), these medications may need to be stopped and intravenous or subcutaneous shorter-acting heparin begun in the hospital before surgery — a process referred to as "bridging." Your doctor will decide whether bridging is necessary based on your heart condition.

Subcutaneous medications

There are two blood-thinning medications: heparin and low-molecular-weight heparin. Both can be injected just underneath the skin. This is sometimes done if it's required for a longer time (e.g., during pregnancy) and eliminates the need for an intravenous line long-term. If you need heparin or low-molecular-weight heparin, blood tests are required to check that the dose is correct. Heparin is safe for use in pregnancy.

Your cardiologist will determine which type of blood-thinning medication is best for you. 

Medication and diet interactions with warfarin

Many over-the-counter or prescription medicines can interact with warfarin and change your INR, which can be hazardous. These medicines include most antibiotics, several pain medicines (e.g., non-steroidal anti-inflammatory drugs) and medications for acid reflux such as cimetidine (Tagamet). In general, avoid aspirin when you're being treated with warfarin.

If you're taking warfarin and start a new prescription or over-the-counter medication, check with your health care professional. It's important to determine whether this might affect your INR and if you need more frequent blood testing.

Certain foods also interfere with how your body processes warfarin. Your cardiologist will discuss foods to avoid or eat regularly while taking warfarin. If you're on warfarin, always ask your health care professional about your diet and before taking any other medicines, including vitamins and herbal preparations. Read more about warfarin.

Anticoagulation in pregnancy

Women who require anticoagulation and become pregnant need to take special precautions. Warfarin poses significant risk to the fetus, especially in the first trimester.  Women on warfarin are switched to heparin during the first weeks of pregnancy. Some may then stay on heparin throughout the pregnancy and delivery. Others may be started back on warfarin during the middle of the pregnancy, then switched back to heparin for the delivery.

It's critical to discuss management of anticoagulation during pregnancy with your cardiologist and obstetrician. Care must be tailored for each woman.