[1][3] Common side effects include dizziness, problems seeing, shortness of breath, chest pain, and tiredness.

[1] It works by decreasing the entry of sodium in heart cells, causing prolongation of the cardiac action potential.

[9][10] In individuals suspected of having the Brugada syndrome, the administration of flecainide may help reveal the ECG findings that are characteristic of the disease process.

[12] Results of a medical study known as the Cardiac Arrhythmia Suppression Trial (CAST) demonstrated that patients with structural heart disease (such as a history of MI (heart attack), or left ventricular dysfunction) and also patients with ventricular arrhythmias, should not take this drug.

[17][18] Due to the narrow therapeutic index of flecainide, physicians should be alert for signs of toxicity before life-threatening arrhythmias occur like torsades de pointes.

Signs of flecainide toxicity include marked prolongation of the PR interval and widening of the QRS duration on the surface ECG.

There may be signs and symptoms attributable to overt heart failure secondary to sudden decreased myocardial contractility.

Placing the individual on cardiopulmonary bypass support may be necessary in order to temporarily remove the need for a beating heart and to increase blood flow to the liver.

[23][24][25][26][27] Flecainide has high bioavailability after an oral dose,[28] meaning that most of the drug that is ingested will enter the systemic blood stream.

[31] Flecainide works by blocking the Nav1.5 sodium channel in the heart, slowing the upstroke of the cardiac action potential.

[33] Flecainide also inhibits ryanodine receptor 2 (RyR2),[34] a major regulator of sarcoplasmic release of stored calcium ions.

[35] While Flecainide therapy has been shown to suppress ventricular arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) and mouse models of this disease, the relative contribution from the inhibition of sodium channels and of RyR2 in this effect on CPVT is unclear.

In addition to being marketed as Tambocor, it is available in generic version and under the brand names Almarytm, Apocard, Ecrinal, and Flécaine.