Final answer:
Systolic blood pressure represents the maximum pressure in the arteries, which occurs when the heart contracts during systole. It is the first number in the blood pressure measurement, such as the 120 in a 120/80 mm Hg reading.
Step-by-step explanation:
Systolic blood pressure is the pressure in the arteries when the heart contracts. This is the maximum pressure in the arteries and occurs during the cardiac cycle known as systole. Systolic pressure is typically indicated as the first number in a blood pressure measurement, for example, 120 in a reading of 120/80 mm Hg, and it can be in the range of 100 to 200 mm Hg with a desirable range being 100 to 120 mm Hg.
Therefore, the correct answer to the question "Systolic blood pressure is the pressure when the:" is B. heart contracts. This phase involves the ejection of blood from the heart into the circulatory system, leading to the stretch of artery walls to accommodate the surge of blood, thus reflecting the highest pressure reached during the pumping action of the heart.