Most patients with an overdose of diphenhydramine, an H1 antihistamine, manifest hypertension and tachycardia.[60] In normotensive subjects, sustained postexercise vasodilatation is abolished by combined oral H1R and H2R antagonists, fexofenadine and ranitidine.[61] The incidence of cardiovascular‐related treatment‐emergent adverse events, including tachycardia and increased heart rate, appears to exhibit a dose‐related trend in the patients treated with bavisant, a highly selective H3R antagonist.[62] Therefore, H1R, H2R, and H3R may not be promising targets for cardiovascular diseases. This evidence concerns the gene HRH2 and cardiovascular disorder.