Spinal anesthesia is commonly used in cesarean section surgeries . The most important adverse effects of spinal anesthesia are hypotension and bradycardia caused by sympathetic blockade, with an incidence of about 55-100% . However, blocking the venous return by the gravid uterus increases the risk of hypotension. Spinal anesthesia-induced hypotension is commonly associated with uncomfortable symptoms, such as shivering , nausea and vomiting, in the mother. Prolonged maternal hypotension may lead to serious maternal adverse effects, such as cardiovascular collapse, loss of consciousness, apnea, and aspiration of gastric contents. In addition, uteroplacental blood flow decreases in cases of sustained hypotension and detrimental neonatal effects, such as fetal acidosis and fetal death, may occur. Preventing spinal anesthesia-induced hypotension during cesarean section is essential for the well-being of both the mother and neonate.

Also, Shivering often happens after spinal anesthesia. Shivering is an unconscious and rhythmic movement involving several groups of muscles. The increase of muscle activity generates the elevation of oxygen consumption, lactic acidosis, and carbon dioxide production In recent years, researchers have focused on the effects of the Bezold-Jarisch reflex (BJR) . This reflex includes a triad of bradycardia, hypotension, and apnea. Researchers have suggested that serotonin and 5-hydroxytryptamine 3 (5-HT3) receptors play an important role in the occurrence of the BJR after spinal anesthesia . The 5-HT3 receptors are present in the heart, lung, and spine. Diminished venous return caused by spinal anesthesia stimulates the cardiac chemoreceptors, and parasympathetic activity increases, which results in bradycardia and hypotension . Studies have suggested that the use of 5-HT3 antagonists may attenuate spinal anesthesia-induced hypotension, thus inhibiting peripheral vasodilatation, alleviating the BJR, and increasing venous return to the heart . Ondansetron is a commonly used 5-HT3 receptor antagonist, and its peak plasma concentration occurs within 30 min following IV injection. Granisetron is a new 5-HT3 receptor antagonist, and the onset of action occurs 30 min following its IV administration [](streamdown:incomplete-link)

Inclusion Criteria:

• All parturient who underwent elective caesarean delivery under spinal anesthesia will be included in this study

Exclusion Criteria:

• 1. Patient refusal 2. Patient with significant neurological , psychological disease 3. patient known allergy to ondansetron or granisetron, 4. patients receiving serotonin agonists or antagonists, 5. patient ischemic heart disease, chronic hypertension or pregnancy induced hypertension