More knowledge is needed on the biosafety of Ru‐containing compounds, and in particular on their interactions with “anti‐targets” such as hERG or Cav1.2 (cardiac toxicity),[143] the P‐glycoprotein (drug‐drug interactions),[144] or the serotonin receptor 5‐HT2B (valvulopathy and pulmonary hypertension),[145] the blockade of which may cause potentially serious side effects in humans. The gene discussed is KCNH2; the disease is pulmonary hypertension.