It is the LDL that attaches itself to the walls of arteries, forming the plaque that gums up and partially blocks the arteries. This means that the blood has to be pumped through a narrower vessel, which means that blood flow will be impeded, and may give rise to hypertension.

It is the HDL that works against the buildup of LDL plaque on arterial walls. Bengtsson, in one of his studies, found that HGH tended to promote lower levels of LDL (the bad one) while increasing levels of HDL (the good one).

The major consequence of this, one would expect, should be a reduced buildup of plaque on arterial walls.
Oxidative stress has been shown to be a major factor in end organ damage with hypertension.

In a sense, then, HGH has shown itself to be a triple threat against heart disease: it strengthens the heart muscle itself; it appears (thus far) to reduce cell death in the heart that normally follows a heart attack (should we be unfortunate enough to have one); and it lowers the bad cholesterol that tends to collect on arterial walls and obstruct blood flow.