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Resumen: Introducción: La prolongación del intervalo QT se asocia con arritmias ventriculares y muerte súbita. Objetivo: Determinar el valor del intervalo QTc en recién nacidos sanos y evaluar su comportamiento durante los primeros meses de vida. Métodos: Recién nacidos sanos a término de marzo-noviembre 2016 en el Hospital General de Occidente del Estado de Jalisco, México. Se les practicó un electrocardiograma de 12 derivaciones a una velocidad de 25 mm/s durante las primeras 48 h. Se midió el intervalo QT en DII y se calculó el QTc mediante la fórmula de Bazett. Los pacientes a los que se detectó prolongación del QTc en sus primeras 48 h se valoraron al mes con ECG y ecocardiograma. Si persistieron con QTc alargado se revaloraron a los 6 meses con ECG, Holter de 24 h y estudio electrocardiográfico a padres y hermanos. Los que persistieron con QTc alargado se revaloraron a los 9 meses con ECG. Resultados: Se incluyeron 548 pacientes. La media del intervalo QTc al nacimiento fue de 459 ms; durante este período 33 pacientes presentaron un QTc mayor de 470 ms, los cuales fueron evaluados al mes mediante un nuevo estudio electrocardiográfico, obteniendo una media del intervalo QTc de 446 ms. A los 6 meses se evaluaron 16 pacientes, con una media del intervalo QTc de 434 ms. A los 9 meses se evaluaron 6 pacientes, con una media del intervalo QTc de 438 ms, y solo 4 pacientes persistieron con QTc prolongado. Conclusiones: El intervalo QTc en nuestros pacientes es más prolongado en comparación con otras poblaciones y muestra una normalización paulatina. Abstract: Introduction: QT interval prolongation is associated with ventricular arrhythmias and sudden death syndrome. Objective: To determine the value of QTc interval in healthy newborns in a general hospital in Jalisco, Mexico, and their outcome during their first months of life. Methods: The study included healthy newborns from March to November 2016, in the Hospital General of Occidente in Jalisco, Mexico. A 12-lead electrocardiogram was performed at a speed of 25 mm/s during the first 48 h of life. The QT interval was measured in lead DII, and the QTc interval was calculated using the Bazett formula. Patients detected with QTc prolongation were assessed monthly with an ECG and echocardiogram. If they persisted with prolonged QTc interval, they were re-evaluated at 6 months with an ECG, 24 h Holter, and electrocardiography study on parents and siblings. Those who persisted with prolonged QTc interval were evaluated with an ECG at 9 months. Results: The study included 548 patients. The mean QTc interval at birth was 459 ms; during this period 33 patients has a QTc greated that 470 ms; which were evaluated monthly with a new electrocardiographic study, obtaining a mean QTc interal of 446 ms. At 6 months 16 patients were evaluated, with a mean QTc interval of 434 ms. At 9 months, 6 patients were found to have a mean QTc interval of 438 ms, and only 4 patients persisted with a prolonged QTc interval. Conclusions: The QTc interval in our population is prolonged compared to other populations and with a gradual return to normal. Palabras clave: Intervalo QTc, Recién nacido, Arritmias, Electrocardiograma, México, Keywords: QTc interval, Newborn, Arrhythmias, Electrocardiogram, Mexico