Some causes related to cardiovascular disease: Headache is only rarely due to cardiovascular diseases.  Severe hypertension can cause headache, as can certain types of stroke (particularly a catastrophic type of stroke called subarachnoid hemorrhage).

Some causes related to other disorders:  The vast majority of headaches are related to causes other than cardiac. Migraine and so-called "tension" headaches are the most common causes.

Significance: Generally headaches do not have a cardiovascular cause.  The exception, subarachnoid hemorrhage, typically presents with a sudden, explosive onset of absolutely severe head pain, and severe neurological symptoms.  Anyone with these symptoms does not need to be told they need medical help.