Inclusion Criteria:  Diagnoses of Alzheimer's disease according to the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) criteria. Presence of a caregiver (friend or relative) who can assume responsibility for medication administrations, accompany the patient to all visits, and rate patient's condition. Written informed consent form from both the patient (or surrogate) and caregiver. A Mini-Mental State Examination score between 12 and 26 inclusive. Prescription of donepezil (5-10mg/d), rivastigmine (3-6mg/d), galantamine or galantamine ER (8-16mg/d) for a minimum of 4 weeks prior to randomization. Agreement not to take hydralazine. Age 49 and over.  Exclusion Criteria:  Non-Alzheimer primary dementia diagnosis (e.g., vascular dementia, Lewy body dementia, frontotemporal dementia, vitamin B-12 deficiency, hypothyroidism). Diagnosis of any of the following conditions; major depression, delirium, alcohol or psychoactive substance abuse or dependency, schizophrenia, or delusional disorder as defined by Diagnostic and Statistical Manual (DSM)-IV. Diagnosis of systemic illnesses that would interfere with participation in the study or decrease the life expectancy to less than one year. Currently being treated with hydralazine or a history of intolerance to oral therapy with hydralazine Any intravenous treatment for heart failure, except IV furosemide (e.g. IV inotropes, pressors, nitrates or nesiritide) at the time of screening. Systolic blood pressure <100 mmHg, reversible etiology of acute heart failure such as myocarditis, acute myocardial infarction-over the past 4 weeks, arrhythmia and existence of pacing device (Acute myocardial infarction is defined as symptoms and major electrocardiogram (ECG) changes (i.e., ST segment elevations), and arrhythmia includes unstable heart rates above 120/min or below 50/min). Existence of severe congenital heart disease (such as uncorrected tetralogy of fallot or transposition of the aorta) and severe aortic or mitral stenosis or severe rheumatic mitral regurgitation. Concurrent use of phosphodiesterase type 5 (PDE5) inhibitors (e.g. Viagra, Etc.) Cardiac revascularization within the last 3 months or likelihood of requiring coronary revascularization within the study period. eGFR (Glomerular Filtration Rate) < 15ml/min/1.73m2, or on regular dialysis, or planned dialysis within the study period.