Among patients with long QT syndrome (LQTS), disease severity and response to therapy vary according to the genetic mutation involved. Napolitano and colleaguesArticle performed genetic screening in 430 patients with LQTS and 1115 family members and describe the types and prevalence of mutations found. In addition, the authors confirmed their findings by testing for the identified mutations in a separate cohort of patients. Based on their results, the authors propose a strategy for genetic screening for LQTS. In an editorial, KaufmanArticle discusses the clinical importance of patient genotype in LQTS and the efficiency, affordability, accessibility, and accuracy of current genetic tests for LQTS.