 Methods. Approximately 36 healthy adult subjects age-matched to previously studied LQT1 subjects will undergo 1 screening history, 2 two weeks of beta-blocker therapy ending in an exercise test, and 3 two weeks of placebo therapy ending in an exercise test. Beta blocker and placebo will be given in random order in a double-blind fashion. The QT response to exercise and recovery will be compared between drug-free and beta-blocker-treated states. These data will be compared to those previously collected for LQT1 subjects. 