Cardiac autonomic dysfunction and obesity may play a role in the development of higher blood pressure, however the underlying physiological mechanisms are not yet fully understood. This thesis aimed to unravel the factors that influence the cardiac autonomic nervous system (ANS) and to determine the genetic and environmental overlap of blood pressure with cardiac ANS and obesity measures in three large population-based databases. First, I found that age and sex were the most important determinants of the cardiac ANS measures, explaining about 16% of the inter-individual differences. We also established reference values across difference age groups and showed that the function of the cardiac ANS declined substantially with age and that women had a better cardiac ANS function than men. Second, I confirmed that all cardiac ANS and obesity indices were heritable and showed that they significantly correlated with blood pressure. Third, we found significant genetic correlations of the cardiac ANS and obesity indices with blood pressure. In conclusion, our work provides robust evidence that blood pressure is genetically correlated with cardiac ANS and obesity which will drive the scientific efforts to identify genes responsible for these shared genetic influences.