If your systolic blood pressure is elevated but your diastolic is in the normal range, it’s often a sign of what’s called isolated systolic hypertension—a condition especially common in people over 50. This happens when the arteries become stiffer with age, making it harder for blood to flow during each heartbeat. While the bottom number (diastolic) reflects pressure between beats and may stay in range, the top number (systolic) rises as the heart works harder to push blood through less flexible