BACKGROUND The electrocardiographically measured QT interval (QT) is heritable and its prolongation is an established risk factor for several cardiovascular diseases. Yet, most QT genetic studies have been performed in European ancestral populations, possibly reducing their global relevance. OBJECTIVE To leverage diversity and improve biological insight, we fine mapped 16 of the 35 previously identified QT loci(46%) in populations of African American(n = 12,410) and Hispanic/Latino (n = 14,837) ancestry. METHODS Racial/ethnic-specific multiple linear regression analyses adjusted for heart rate and clinical covariates were examined separately and in combination after inverse-variance weighted trans-ethnic meta-analysis. RESULTS The 16 fine-mapped QTlociincludedontheIllumina Metabochip represented 21 independent signals, of which 16(76%) were significantly (P-value100 kb). Finally, bioinformatics-based functional characterization suggested a regulatory function in cardiac tissues for the majority of independent signals that generalized and the novel SNPs. CONCLUSION Our findings suggest that a majority of identified SNPs implicate gene regulatory dysfunction in QT prolongation, that the same loci influence variation in QT across global populations, and that additional, novel, population-specific QT signals exist.