Final answer:
When diastolic blood pressure rises, it indicates increasing pressure on the arterial walls during ventricular relaxation, potentially straining the heart.
Step-by-step explanation:
When the diastolic blood pressure increases, it is a sign of increasing pressure on the walls of the arteries during ventricular relaxation, or diastole. This can indicate that the blood vessels are not dilating properly to pass blood through, which can strain the heart in its attempt to pump blood.