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Atrial fibrillation (AF), the most common cardiac arrhythmia, is characterised by rapid and irregular contraction of the atrium. The risk of AF increases with age and AF increases the risk of various heart disorders, stroke and mortality. AF can occur in a sporadic or familial form. The underlying mechanism leading to AF is not well known but genetic analysis can increase our insight into the molecular pathways in AF. Detailed information on the molecular mechanisms of a disorder increase options for diagnosis and treatment. Recently, a gain-of-function mutation in exon of the KCNQ1 gene located on chromosome 11 was identified in a large Chinese AF family. KCNQ1 associates with KCNE1 or KCNE2 (both located on chromosome 21) to form cardiac potassium channels. Subsequent analysis of Chinese families showed a KCNE2 mutation in two families. Other genetic studies show linkage to chromosome 6 and 10, indicating genetic heterogeneity. A number of studies have shown that altered expression of the atrial connexin40 protein is a risk factor for AF. Connexin genes encode gap-junction proteins that are important in cardiac conduction and for normal wave propagation.In this study we analysed the role of KCNQ1, KCNE1 coding region and Cx40 promoter region in six Dutch AF families by sequence analysis.No mutations were found in these genes. The absence of mutations indicates genetic heterogeneity in familial AF; however, further research is needed. Candidate genes are being sequenced, linkage analysis in a large family will be performed and additional AF families will be collected.