We investigated the relation between heart rate and the QT interval using face immersion in cold water in children with long QT syndrome (LQTS) without a family history of this condition, and in control children. The face immersion test revealed that all children with high probability of LQTS had a significantly longer QT interval than control children during face immersion, and that the test could induce T-wave alternans or a notched T-wave in all children with a high probability of LQTS.