To date, 3 studies have performed eQTL mapping to attempt to identify SNP modulators of gene expression within the atrial tissue. The initial study by Lin et al15 evaluated genome-wide eQTLs using 53 right and 52 left atrial appendage tissue samples obtained from heart failure patients undergoing transplant and unused donor hearts with normal left ventricular function. In addition to identifying 187 and 259 statistically significant cis-eQTLs in the right and left atrial tissue, respectively, they found that the AF GWAS SNP within the 10q22 locus impacted gene expression of the more distantly located MYOZ1 gene rather than the adjacent SYNPO2L gene. A subsequent analysis by the group from the current study evaluated for an association between SNPs within the 4q25 region, the locus most strongly associated with AF in GWAS analyses, and transcript levels of PITX2, the gene residing closest to these signals. 16 Of note, PITX2 has multiple splice variants with prior work showing that PITX2c is the primary splice isoform expressed in left atrial tissue. 17 Surprisingly, no associations between the 4q25 SNPs and PITX2c transcript levels were identified among 239 left atrial appendage tissue samples. 16 The most recent study by Martin et al18 involved 122 right atrial appendage samples and focused on 9 AF GWAS SNPs and 16 candidate genes residing within their loci. Investigators found significant cis-eQTLs for PITX2a (the primary right atrial splice isoform), MYOZ1, CAV1, C9orf3, and