There are many available resources. I'd look at
http://www.scuba-doc.com/hyptdiv.htm as well as DAN's website
http://www.diversalertnetwork.org/medical/faq/faq.asp?faqid=64
Unless quite high, hypertension by itself isn't a problem for diving, and of course can usually be controlled with medications and/or lifestyle changes. But it is one of many risk factors for coronary artery disease, which probably causes more diving deaths than any other single factor. So you should be evaluated for other risk factors (i.e. diabetes, high cholesterol, smoking, family history, etc.), and thus the overall risk of CAD. If you are higher risk, studies such as treadmills may need to be done prior to diving.
Hypertension that is related to other diseases such as kidney disease, raises all sorts of other issues related to the underlying disease.
Meds are another issue. Beta blockers are of concern, as they inhibit the rise in heart rate with exercise, which could interfere with maximal physical exertion--it's quite variable depending on the dose and the individual. Some people can experience fatigue, or even mental changes with these. Obviously that's a concern for diving. Older drugs such as methyldopa and clonidine, not widely used anymore, can cause drowsiness. Diuretics can cause electrolyte imbalances, and of course we're always telling divers to hydrate, so they aren't the best choice for most divers.
Good luck.
