37 DZ and 12 MZ twin pairs underwent a clinical and ECG heart examination. As to their zygosity, it is suggested that a concurrent similar clinical finding, very similar ECG and a mean intrapair difference of corresponding unipolar chest lead waves d ≤ 1.5 definitely support monozygosity.
Paired analysis of the ECG curves shows that the difference between MZ and DZ twins is best characterized by Tv1-6 and, to a certain extent, by Rv1-6. The same applies — in partial agreement with Mathers et al. — for PQ and QTc intervals.
Considering the intrapair differences in both MZ and DZ twins, it was found that they tend to increase in the course of one cardiac cycle, thus indicating a gradual prevalence of peristatic factors.