Peripartum cardiomyopathy (PPCM) is a diagnosis of exclusion in women presenting with heart failure due to left ventricular (LV) systolic dysfunction. PPCM should be considered in case of unknown etiology of heart failure during pregnancy or after childbirth. Long QT syndrome is a primary electrical heart disease associated with a prolonged QT interval on the ECG, recurrent paroxysms of ventricular tachycardia, and a high risk of sudden death. Our aim was to demonstrate a case of cardiomyopathy in combination with long QT syndrome in a patient with a mutation in the FLNC gene. A 38-years-old woman was hospitalized 4,5 months after childbirth after sudden cardiac arrest and successful cardiopulmonary resuscitation. Long QT interval was revealed on the electrocardiogram. Echocardiography registered an akinesis of the apical and middle segments of the anterior wall of the left ventricle and interventricular septum, apex, left ventricular ejection fraction – 32%. Coronary angiography revealed no stenotic lesion of the coronary arteries. N-terminal precursor of brain natriuretic peptide (NTproBNP) was 33300 mg/l. Mass parallel sequencing of 17 genes revealed the nucleotide variant c.1609T>G (chr7:128480661T>G, NM_001488.4; rs760471547) in a heterozygous state in exon 10 of the FLNC gene (OMIM 102565), leading to the amino acid variant p.Y537D.The combination of peripartum cardiomyopathy and long QT syndrome may increase the likelihood of sudden cardiac death, especially in individuals with a genetic mutation of cardiomyopathy. Timely diagnosis of the described conditions is necessary to prevent complications and increase the life expectancy of patients.