Objective: To describe the kinetic profile of arrhythmia in pregnant women with heart diseases in different cardiovascular risk according to mWHO classification. Design: Prospective observational study Setting: Cardiac and Vascular Diseases, Institute of Cardiology, CMUJ, John Paul II Hospital, Krakow, Poland Population: 103 pregnant women with organic heart disease(HD) Methods: 24-hour ECG-Holter was obtained in each trimester of pregnancy and post-partum period Main outcome measures: Supraventricular arrhythmia(SA): supraventricular tachycardia (SVT), supraventricular extrasystole (significant when SVE >30/hour), atrial tachycardia (AT), atrial fibrillation (AF);Ventricular arrhythmia(VA): ventricular premature contractions (PVCs >30/h), non-sustained, sustained tachycardia (nsVT, sVT);Conduction disturbances: low grade: AV I degree block, Mobitz I, high grade: Mobitz II,III degree blocks. Results: The prevalence of arrhythmia was 45.6 % of women, SA occured in 24.3 % and VA in 31.1%. Episodes of nsVT were more common in women with serious HD (mWHO class II-II, III, IV) than in women with milder HD (mWHO I, II) in each trimester: trimester1: 1,7% vs. 13,6%, p=0,02; trimester2: 5,1% vs. 18,2%, p=0,03; trimester3: 2,3% vs. 13,9 %, p=0,04,respectively.The kinetic profile of arrhythmia throughout pregnancy was different among groups: ventricular arrhythmia had tendency to increase in both groups, supraventricular arrhythmia declined in women with milder CHD and increased in serious CHD group. The highest rate of arrhythmia was in the 2nd trimester in both groups (29,2%). Conclusion: The kinetic profile of arrhythmia during pregnancy was different between groups with lower and higher cardiac risk, with more favorable profile in lower cardiac risk group. Keywords: Arrhythmia, Cardiovascular disease, Pregnanc