No, high blood pressure is not considered heart disease, but it is one of the signs and symptoms that may lead to heart disease if it is not corrected.
High blood pressure over a period of many years may lead to hardening of the arteries, which forces the heart to work harder than it would otherwise need to in order to pump blood through the vascular system.
This may cause the heart to enlarge over time in order to compensate for the extra work load that has been placed upon it. An enlarged heart or hardened arteries, for example, are both considered symptoms of heart disease.
So, high blood pressure in another itself is not heart disease, but it will most likely lead to heart disease if steps are not taken to get blood pressure levels into the normal range.
This is normally accomplished through a combination of dietary changes and exercise, as well as other lifestyle changes. Prescription medication is an option, as well, when necessary.