EDN1 and Arrhythmia: Dong et al. (2004) have identified at least one allele of the ET-1 gene (T1370G single nucleotide polymorphism) that confers an increased risk of left ventricular hypertrophy in response to environmental stress. Finally, ET-1 evokes cardiac mast cell degranulation (Murray et al. 2004), which can be arrhythmogenic. Indeed, extensive degranulation of mast cells is observed in healthy Mexico City dogs (Calderón-Garcidueñas et al. 2001a), and arrhythmias have been observed in Mexico City children (Calderon-Garcidueñas L, Hazucha MJ, Herbst MC, Reed W, Cascio WE, unpublished data).