Propafenone is a Class IC anti-arrhythmic that affects the way your heart beats.

Propafenone is used in certain situations to prevent serious heart rhythm disorders.

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

You should not use propafenone if you are allergic to it, or if you have:

• heart failure, or if you have recently had a heart attack;
• a genetic heart condition called Brugada syndrome;
• a serious heart condition such as "sick sinus syndrome" or "AV block" (unless you have a pacemaker);
• severe low blood pressure, or history of slow heart beats that have caused you to faint;
• a severe or uncontrolled electrolyte imbalance; or
• wheezing or shortness of breath.

Tell your doctor if you have ever had:

• a breathing disorder;
• liver or kidney disease;
• lupus;
• myasthenia gravis; or
• an abnormal blood test called Antinuclear Antibody Test or ANA.

Tell your doctor if you have a pacemaker or defibrillator. These devices may need to be re-programmed while you are taking propafenone.

Tell your doctor if you are pregnant or breast-feeding.

This medicine may affect fertility (ability to have children) in men. Talk with your doctor if you have concerns about this risk.

Use Rythmol SR (Oral) exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

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

Propafenone may cause a new or worsening heartbeat pattern. Call your doctor at once if you have fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness (like you might pass out)

Also call your doctor at once if you have:

• shortness of breath (even with mild exertion);
• swelling in your arms or legs;
• sudden weight gain; or
• fever, chills, sore throat.

Common side effects may include:

• irregular heartbeats;
• nausea, vomiting, constipation;
• headache, dizziness, tiredness; or
• unusual or unpleasant taste in your mouth.

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.

Grapefruit may interact with propafenone and lead to unwanted side effects. Avoid the use of grapefruit products.