The incidence of cardiac arrhythmias is estimated et 1.2 per 1000 pregnancies, usually in the third trimester, and 50% of them are asymptomatic. They may appear for the first time in pregnancy, or have a recurring character. An important risk factor related to their appearance is the presence of structural heart disease, which complicates <1% of pregnancies. Generally the symptoms are mild and the treatment is not necessary, but in some cases pharmacotherapy is necessary. Pharmacotherapy must be a compromise between the potentially adverse effects of drugs on the fetus and the beneficial effects on the cardiovascular system of the mother. Due to the development of cardiac surgery many women with heart defects reach reproductive age and become pregnant. Therefore this problem will be faced more and more often in clinical practice. In addition to pharmacological methods some cardiac arrhythmias may require urgent, life-saving procedures. External electrical cardioversion is associated with the application of certain amount of energy via two electrodes placed on the thorax. It is used to treat hemodynamically unstable supraventricular tachycardias, including atrial fibrillation and atrial flutter. Also in hemodynamically stable patients in whom drug therapy was ineffective elective electrical cardioversion can be use to convert cardiac arrhythmia to sinus rhythm. We present a case of a 33 years old patient with congenital heart disease surgically corrected in childhood who had first incident of atrial flutter in pregnancy. Arrhytmia occured in 26th week of gestation. The patient was hemodynamically stable and did not approve electrical cardioversion as a method of treatment therefore pharmacotherapy was started. Heart rate was controled with metoprolol and digoxin, warfarin was used to anticoagulation. Calcium and potassium were also given. Described therapy did not convert atrial flutter to sinus rhythm therefore in 33rd week of gestation after patient`s approval electrical cardioversion was performed. Before cardioversion transesophageal echocardiogram was made to exclude the presence of thrombus inside atria. Energy of 50J was applied and sinus rhythm was restored. Cardiotocography during and after cardioversion did not show any significant fetal heart rate changes. Further pregnancy and puerperium were uneventful. Case report and review of the literature about cardiac arrhytmias and methods of its treatment especially in pregnant women. Analysis of medical documentation of the patient treated in the Department of Cardiology as well as in the Department of Obstetrics and Perinatology Medical University of Lublin. Review of abstracts and papers in the Medline database about heart arrhytmias occuring during pregnancy, methods of their treatment, with special refference to electrical cardioversion. Pregnancy is a condition which predisposes to cardiac arrhytmias. It is associated with changes in cardiovascular system of pregnant women that appear physiologically. They can be effectively treated with low risk for mother and fetus. Electrical cardioversion is an effective and safe method of therapy of supraventricular arrhytmias also during pregnancy. The adaptation of the maternal hemostasis in pregnancy predisposes women to an increased risk of thromboembolism therefore anticoagulant therapy is essential to minimize the risk of embolic episodes and stroke during elective cardioversion. Pregnant women with structural or functional heart diseases should be under supervision of multidiscyplinary team of specialists (obstetricians, cardiologists, neonatologists, pediatricians).