Patients with heart failure are at an increased risk for thiamin deficiency (TD), for many reasons such as malnutrition and the use of diuretic drugs. Thiamin is a B vitamin that plays an important role in the production of energy in body. Therefore, low levels of thiamin may limit the amount of energy available for the heart to pump blood. Recent thiamin supplementation trials have demonstrated significant improvements in heart function. However, while clinically important, the results of these studies are limited by their small sample sizes, indirect measurement of thiamin status and reliance on hospitalized patients. Therefore, the investigators' goal is to determine the prevalence of thiamin deficiency in ambulatory patients with heart failure by direct measurement of thiamin in red blood cells.