You should not use this medication if you are allergic to propafenone, or if you have untreated or uncontrolled congestive heart failure, a heart condition called "sick sinus syndrome” or "AV block” (unless you have a pacemaker), slow heartbeats or severely low blood pressure, an electrolyte imbalance, or a breathing disorder such as asthma.
Before you take propafenone, tell your doctor if you have congestive heart failure, liver or kidney disease, lupus, arthritis, myasthenia gravis, or if you have had a heart attack within the past 2 years.
You will need to receive your first few doses of propafenone in a hospital setting in case the medication causes serious side effects. Your heart rate will be constantly monitored using an electrocardiograph or ECG (sometimes called an EKG). This machine measures electrical activity of the heart.
Call your doctor at once if you have a serious side effect such as weak pulse, slow breathing, feeling like you might pass out, feeling short of breath, swelling, rapid weight gain, pale skin, easy bruising or bleeding, unusual weakness, confusion, unusual thoughts or behavior, or seizure.