Isradipine (tradenames DynaCirc, Prescal) is a calcium channel blocker of the dihydropyridine class. It is usually prescribed for the treatment of high blood pressure in order to reduce the risk of stroke and heart attack. Except for diuretic activity, the mechanism of which is not clearly understood, the pharmacodynamics effects of isradipine observed in whole animals can also be explained by calcium channel blocking activity, especially dilating effects in arterioles, which reduce systemic resistance and lower blood pressure, with a small increase in resting heart rate. Isradipine binds to calcium channels with high affinity and specificity and inhibits calcium flux into cardiac and arterial smooth muscle cells. It exhibits greater selectivity towards arterial smooth muscle cells owing to alternative splicing of the alpha-1 subunit of the channel and increased prevalence of inactive channels in smooth muscle cells. Although like other dihydropyridine calcium channel blockers, isradipine has negative inotropic effects in vitro; studies conducted in intact anesthetized animals have shown that the vasodilating effect occurs at doses lower than those do which affect contractility. In patients with normal ventricular function, isradipine's afterload reducing properties lead to some increase in cardiac output. Effects in patients with impaired ventricular function have not been fully studied. Most adverse reactions were mild and related to the vasodilatory effects of isradipine (dizziness, edema, palpitations, flushing, tachycardia), and many were transient. About 5% of isradipine patients left studies prematurely because of adverse reactions (vs. 3% of placebo patients and 6% of active control patients), principally due to headache, edema, dizziness, palpitations, and gastrointestinal disturbances.