What is the heart doing when a person has high blood pressure?

Pumping: But it's pumping against a higher total peripheral resistance which in time can cause a reduction in the strength of contraction (ejection fraction) and eventually leads to congestive heart failure (over many years).

More resistance.: The heart is working harder to pump blood through a high pressure system. Over time, this leads to remodeling and thickening of the heart muscle. This is similar to your biceps getting bigger when you do weight resistance training. Difference is, the arm gets stronger with bigger muscles, whereas the heart runs into lots of problems when its normal architecture is disrupted.