Nielsen R, et al. - In patients with heart failure and reduced ejection fraction (HFrEF), researchers intended to modulate circulating 3-hydroxybutyrate (3-OHB) levels and assess the alterations in cardiac output (CO), if there was a dose-response link between 3-OHB levels and CO, how the myocardial external energy efficiency (MEE) and oxygen consumption were influenced, and if there was a difference between HFrEF patients and age-matched volunteers in terms of cardiovascular response. According to the findings, 3-OHB offered beneficial hemodynamic impacts without impairing MEE. In the physiological concentration range of circulating 3-OHB levels, these beneficial impacts were measurable. Both HFrEF patients and age-matched volunteers were affected by 3-OHB hemodynamically. In HFrEF patients, 3-OHB may potentially be part of a new treatment principle.