Diastolic pressure is the pressure trough or low generated as the 1) superior vena cava contracts. 2) ventricles relax. 3) pulmonary artery recoils. 4) ventricles contract.

To determine the correct answer regarding diastolic pressure, let's analyze the options provided: 1. **Superior vena cava contracts**: The superior vena cava is a large vein that carries deoxygenated blood from the upper body to the heart. Its contraction does not directly relate to diastolic pressure. 2. **Ventricles relax**: Diastolic pressure is defined as the pressure in the arteries when the heart ventricles are relaxed and filling with blood. This is the correct relationship. 3. **Pulmonary artery recoils**: While the pulmonary artery does have some elastic recoil, this is not the primary factor that defines diastolic pressure. 4. **Ventricles contract**: This refers to systolic pressure, which is the pressure in the arteries when the ventricles are contracting and pumping blood. Based on this analysis, the correct answer is: **2) ventricles relax.**