Great improvements have been made in treating heart conditions, largely due to the research and development of new medicines. This information describes some of the different medicines often prescribed for people with a heart condition – such as angina, heart attack, heart failure, heart rhythm disorders and heart valve disease. It also covers medicines used to control high blood pressure or to lower cholesterol levels and those used to prevent blood clots from forming. This page explains why you may have been given each medicine and how it works. It also describes the most common side effects.

This information is in conjunction to the advice that your doctors, pharmacists or nurses may give you based on their knowledge of your condition but it should help you to understand what they tell you.

Anticoagulants - heparin, warfarin

Blood clots are made up of platelets (tiny blood cells clumped together) and a protein called fibrin. If a clot is not treated, it could travel to the brain and cause a stroke, or travel to the lung and block a main artery (pulmonary embolism). Anticoagulants prevent fibrin from forming and so prevent harmful blood clots from forming. They are most commonly prescribed for people who have an abnormal heart rhythm, such as atrial fibrillation, or for those who have an artificial heart valve, as both these conditions increase the risk of having a stroke. Anticoagulants are also essential for treating clots that have already formed, such as those that develop in the veins of the legs (deep-vein thrombosis).


Heparin is injected into a vein and has an immediate effect in preventing further blood clots from forming. This is known as intravenous heparin, and is usually given in hospital.

Another form of heparin called ‘low molecular weight heparin’ may be given subcutaneously (by injection just under the skin) over a longer period of time. This can be continued once the person returns home if it is needed. Some people can do the injection themselves, and sometimes a nurse or other health professional will do it.


Warfarin is an anticoagulant that is given when long-term prevention of blood clotting is needed. This medicine is most often used for people with an irregular heart rhythm, such as atrial fibrillation (AF). It may also be given to people with heart valve disease, especially those who have had a heart valve replacement using a mechanical valve.

Warfarin makes the blood thinner so that it doesn’t clot so easily. While you are taking warfarin, you will need to have regular blood tests to measure your INR, to make sure that the clotting activity of the blood is within safe but effective levels. ‘INR’ stands for International Normalised Ratio and is a way of measuring the time it takes for your blood to clot. The person who prescribes your warfarin will decide what dose to give you based on the result of your INR test. In the beginning, you may need to have your INR checked almost every day, but later on it will be done usually every four to eight weeks.

If you’re taking anticoagulants, you should always carry an Anticoagulant card and remember to tell anyone treating you that you are taking anticoagulants. (An Anticoagulant card is a small card that you can show to anyone treating you, to tell them that you are taking anticoagulants.) There is usually a card in your anticoagulation treatment booklet.

The amount of warfarin there is in your bloodstream can change very quickly and what you eat can also have an effect on this. Avoid cranberry juice and cranberries as they can increase the effect of warfarin, and so increase the risk of bleeding. If you’re taking warfarin and have cranberry juice or cranberries by mistake, contact your GP or anticoagulation clinic to have your blood checked, and to find out if your dose needs to be adjusted.

Foods that are high in vitamin K – such as liver, Brussels sprouts and broccoli – can prevent warfarin from working as it should. But it’s important that you eat a variety of fruit and vegetables. If you’re taking warfarin, don’t stop eating foods that are high in vitamin K. Just try and make sure you eat them regularly, rather than having them only every now and then. Having them regularly shouldn’t make a difference to your warfarin levels, as the amount of vitamin K in your bloodstream will stay fairly constant.

Alcohol can affect the level of warfarin in your bloodstream, so it is important to keep the amount of alcohol you have very low and avoid binge drinking. Long-term use of alcohol can reduce how well the warfarin works.

Oral anticoagulants interact with a number of other medicines including antibiotics, aspirin, ibuprofen and cimetidine, and also with some medicines used to treat arthritis, gout, epilepsy, high cholesterol and abnormal heart rhythms.

The main side effect of taking anticoagulants is bleeding. This happens because the anticoagulants affect the blood-clotting process, to help prevent blood clots from forming. The anticoagulants may cause internal bleeding, or make bleeding from a minor injury worse. This is more likely to happen if your INR level is too high.

Any of the following symptoms could mean that your dose of anticoagulants may be too high. Report these immediately.

• Cuts which bleed for longer than normal.

• Bleeding that does not stop by itself.

• Nose bleeds that last for more than a few minutes. (If a nose bleed lasts for more than 20 minutes, you must go to your GP’s surgery or to the accident and emergency department of a hospital.)

• Bleeding gums.

• Severe bruising.

• Red or dark-brown urine.

• Red or black bowel movements.

• For women, heavier bleeding during periods

This information should be read is in conjunction to the advice that your doctors, pharmacists or nurses may give you about your medication based on their knowledge of your condition but it should help you to understand what they tell you. Please ask your doctor if you have any questions at all about your medications.