Suzuki T, Yazaki Y, Voors AA, et al. - This study was undertaken to determine if levels of trimethylamine N-oxide (TMAO) are responsive to guideline-recommended treatment and medications, and further, reflect changes in outcomes. Levels of TMAO were examined in the systems BIOlogy Study to TAilored Treatment in Chronic Heart Failure (BIOSTAT-CHF), which addressed response to guideline-recommended pharmacological treatment. TMAO levels showed strong associations with adverse events (mortality and/or rehospitalisation) at 1, 2 and 3 years in 2,234 patients with new-onset or progressively worsening HF. In BIOSTAT-CHF, TMAO levels were linked to adverse outcomes and did not respond to guidance-based pharmacological treatment as opposed to BNP levels that did as expected. Lower levels of TMAO were associated with positive outcome irrespective of treatment.