<p>Allergic reactionsto organic nitrates are extremely rare,but they do occur. Nitroglycerin Injection is contraindicated in patients who are allergic to it. In patients with pericardial tamponade, restrictive cardiomyopathy, or constrictive pericarditis, cardiac output is dependent upon venousreturn. Intravenous nitroglycerin is contraindicated in patients with these conditions.</p>