The Human Genome and Haplotyping mapping projects provide powerful new technologies for identifying gene variations that contribute to complex conditions like the susceptibility to sudden cardiac death (SCD). “Genomic” approaches to SCD, in contrast to “genetic” views focused on “high-impact” mutations in a small number of genes, seek to identify minor variations in many different DNA sequences, each of which may convey subtle dimensions of arrhythmia risk in heart disease. Just as family- based linkage studies on the monogenic Mendelian syndromes, like the various long QT conditions, facilitated diagnosis of rare arrhythmias in families, genomics promises insight into the “low-impact” variations distributed widely throughout the population. Clinical applications, eg, in risk stratification, therapy selection, and SCD prevention, are anticipated in the very foreseeable future...