Increased arterial stiffness and blood pressure are characteristic of humans and adult mice with reduced elastin levels caused by aging or genetic disease. Direct associations have been shown between increased arterial stiffness and hypertension in humans, but it is not known whether changes in mechanical properties or increased blood pressure occur first. Using genetically modified mice with elastin haploinsufficiency (Eln(+/-)), we investigated the temporal relationship between arterial mechanical properties and blood pressure throughout postnatal development. Our results show that some mechanical properties are maintained constant regardless of elastin amounts. The peak diameter compliance for both genotypes occurs near the physiologic pressure at each age, which acts to provide maximum pulse dampening. The stress-strain relationships are similar between genotypes and become nonlinear near the systolic pressure for each age, which serves to limit distension under high pressure. Our results also show that some mechanical properties are affected by reduced elastin levels and that these changes occur before measurable changes in blood pressure. Eln(+/-) mice have decreased aortic diameter and compliance in ex vivo tests that are significant by postnatal day 7 and increased blood pressure that is not significant until postnatal day 14. This temporal relationship suggests that targeting large arteries to increase diameter or compliance may be an effective treatment for human hypertension.