Doxacard contains Doxazosin mesylate, a quinazoline compound, is an alpha blocker used to treat high blood pressure and benign prostatic hyperplasia. It is an alpha-1 adrenergic receptor blocker that inhibits the binding of norepinephrine to alpha receptors in the autonomic nervous system. The primary effect of this blockage is relaxed vascular smooth muscle tone decreases peripheral vascular resistance, leading to decreased blood pressure.