Yeah it raises heart rate and blood pressure bc it dilates your blood vessels. The raised HR/BP are to counter that so you keep pushing the same amount of O2 per unit time.
That's one of the reasons. The primary reason is THC is a partial CB1 receptor agonist - CB1 is abundant in the central and peripheral nervous systems - so it increases sympathetic nervous system activity and norepinephrine, both of which raise heart rate independent of vasodilation.