Suppression of this reflex by ondansetron leads to tachyarrhythmias.[1] Thirdly, in some cases, 5HT3  receptor blockade could possibly lead to unopposed action of 5HT2  and 5HT4  receptors, resulting in tachyarrhythmias and hypertension.[1]. The gene discussed is HTR2A; the disease is hypertensive disorder.