MTHFR and Patent foramen ovale: Among PFO subjects with tunnel length/height ratio below 3.5 (n = 20), 4 patients carried the 677 T/T mutation, 4 patients carried the 677 C/T + 1298 A/C double heterozygous mutation, 1 patient carried the 677 C/T heterozygous genotype, 4 patients carried the 1298 C/C homozygous genotype, and 7 patients carried the 1298 A/C MTHFR genotype.