Heart failure (HF) is the main cause of death in middle-aged and older people and is characterized by high morbidity, high mortality, a high rehospitalization rate, and many high-risk groups. Nicotinamide adenine dinucleotide (NAD+) is widely present in the mitochondria of cardiomyocytes and maintains the redox balance in the body, which can effectively treat HF. We sought to evaluate whether NAD+ therapy has some clinical efficacy in patients with HF. Based on using conventional drugs to treat HF, patients (n = 60) were randomized 1:1 to saline and 50 mg NAD+ with 50 mL of normal saline for 7 days. The baseline characteristics of patients before and after treatment and cardiac function (N-terminal pro B-type natriuretic peptide (NT-proBNP) level and left ventricular ejection fraction (LVEF) value) were analyzed. Serological analysis (sirtuin-1 (SIRT1), sirtuin-3 (SIRT3), sirtuin-6 (SIRT6), reactive oxygen species (ROS), and endothelin) was also performed. Among the 60 patients with HF who were treated with NAD+ for 7 days, the improvement rate in NT-proBNP levels and LVEF values was better than in the saline group, although not statistically significant. These patients were more likely to benefit from NAD+ because of higher levels of anti-oxidative stress (SIRT1, SIRT3, SIRT6, and ROS) and anti-endothelial injury (endothelin) than those in the saline control group. According to the results of this study, it is believed that 7 days of NAD+ injections has a positive effect on improving cardiac function, oxidative stress, and endothelial injury in patients with HF compared with the saline control. Chinese Clinical Trial Registry (http://www.chictr.org.cn/) ChiCTR2300074326; retrospectively registered on 3 August 2023.