The term "ventricular diastole" refers to one phase of a biologic activity known as the cardiac cycle, which is one complete heartbeat, during which the ventricles of the heart are relaxed. The heart muscle is divided into four chambers: right atrium, left atrium, right ventricle and left ventricle. Its upper chambers are the two atria, also called auricles, and its two lower chambers are called ventricles. There is much activity involved in one complete cardiac cycle, but it can be divided into two broad phases: diastole and systole.
During ventricular diastole, not only are the ventricles relaxing, they also are filling with blood in preparation for the next phase of the cardiac cycle. There is a significant amount of pressure created in the arteries, and it is necessary for adequate circulation of blood throughout the entire body. Although blood is said to flow throughout the blood vessels of the body, a more accurate description might be that the blood pulsates through the arteries in forceful, rhythmic waves — this creates a pulse that can be felt at certain locations on the body. This is why there are periods of relaxation such as ventricular diastole.
Taking a person's blood pressure is closely related to the subject of ventricular diastole. Blood is forcefully pumped out into circulation with each contraction of the left ventricle, which is a different phase of the cardiac cycle. When the left ventricle is relaxed and refilling with blood, the period of the cardiac cycle known as ventricular diastole is the pressure that is left in the arteries. This pressure is recorded and is called the diastolic blood pressure. The recording of this vital sign itself is an indirect measurement of diastole.
Although recording the pressure remaining in the arteries at the time of the relaxation of the left ventricle might not seem important, abnormal readings can indicate serious health conditions. This is why taking blood pressure with a stethoscope is always preferred over taking this vital sign by palpation. A blood pressure measurement obtained by palpation cannot reveal the pressure remaining in the arteries during ventricular diastole, so it is less accurate information about what is going on inside of the body.