Adenosine is a naturally occurring substance that relaxes and dilates blood vessels. Adenosine also affects the electrical activity of the heart.

Adenosine is used to help restore normal heartbeats in people with certain heart rhythm disorders.

Adenosine is also used during a stress test of the heart.

Adenosine may also be used for purposes not listed in this medication guide.

Before receiving adenosine, tell your doctor if you have asthma or other breathing problems, or if you have ever had a seizure.

Before your heart stress test: Avoid coffee, tea, cola, chocolate, energy drinks or other sources of caffeine. They can interfere with the results of your test.

Adenosine is given as an infusion into a vein. A healthcare provider will give you this injection.

You may receive only one dose of this medicine. Repeat doses may be given if needed to restore normal heartbeats.

Your breathing, blood pressure, oxygen levels, and other vital signs will be watched closely.

Your heart rate will be constantly monitored using an electrocardiograph or ECG (sometimes called an EKG). This will help your doctor determine how long to treat you with adenosine.

You should not be treated with adenosine if you have a serious heart condition such as "sick sinus syndrome" or "AV block" (unless you have a pacemaker), or slow heartbeats that have caused you to faint.

Your doctor will perform tests to make sure you do not have conditions that would prevent you from safely receiving adenosine.

Tell your doctor if you have ever had:

• asthma, COPD, bronchitis, emphysema, or other breathing problems;

• seizures; or

• angina (chest pain).

It is not known whether this medicine will harm an unborn baby. Tell your doctor if you are pregnant.

Tell your doctor if you are breast-feeding. You may need to stop nursing for a short time after you receive adenosine.

Adenosine is usually given as a single dose in a medical setting and does not have a daily dosing schedule.

Since adenosine is given by a healthcare professional in a medical setting, an overdose is unlikely to occur.

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Tell your caregivers right away if you have:

• severe shortness of breath;

• chest pain or tightness, pain spreading to your jaw or shoulder;

• fluttering in your chest;

• a light-headed feeling, like you might pass out;

• a seizure;

• severe headache, blurred vision, pounding in your neck or ears; or

• sudden numbness or weakness, problems with vision or speech.

Common side effects of adenosine may include:

• flushing (sudden warmth, redness, or tingly feeling);

• chest pressure, shortness of breath;

• nausea;

• headache, dizziness; or

• discomfort in your neck or jaw.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Tell your doctor about all your other medicines, especially:

• aminophylline;

• digoxin;

• dipyridamole;

• theophylline; or

• verapamil.

This list is not complete. Other drugs may affect adenosine, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.