High blood pressure leads your heart to work hard constantly, with two long-term effects:

• you get an enlarged heart, which can actually lead to less efficient beating - there's only so much room in there, so a larger heart has less room in which to beat;
• your blood vessels never get a chance to relax, so they tend to harden, meaning that the higher pressures are progressively experienced further away from your heart.

Harder, stiffer blood vessels are more prone to breaking and tearing. They're also more prone to damage that leads to clotting, but the clots don't stick as well. Your risk of strokes rises.

As time passes and your heart spends years working much harder than it was designed for, the muscle starts to degrade, so eventually you have this rather large yet, paradoxically, very weak heart that beats ineffectively. Your blood vessels are trashed all the way out to the capillaries, and between that and the ineffective beating you're not getting adequate oxygen to your extremities. the only fix we have, and it's not a good one, is total heart replacement - organ transplant.