Cardiac output increases during pregnancy and total peripheral resistance decreases resulting in a lower systemic arterial pressure. It is unknown whether pregnancy results in a decrease in mean arterial pressure in long necked animals (llama, giraffe); whether mean arterial pressure (MAP) and heart rate (HR) change in response to variations in the height of the head above the heart and whether the cholinergic system plays a role in this response. MAP and HR were measured in three term pregnant llamas at 4400 meters above sea level through a catheter placed into the descending aorta and connected to Statham P23 Db pressure trasducer and Gilson IOM-5 polygraph. Measurements were done 24-36 hours after catheter placement; at rest (more than 60 cm above heart level) and three times during 120 seconds for each position of the head: Up (U = + 60 cm above heart level). Down (D = - 60 cm below heart level), before and after the administration of an i.v. bolus of atropine (0.2 μg/Kg). At rest without manipulating the neck, MAP was 86.7 ± 14.9 mm Hg and HR was 84 ± 61/min. Results were: ([xmacr ] ± S.D., ANOVA for reapeted measurements and Newman - Keuls test).Pregnant llamas have a lower MAP (86.7 nm Hg) than non pregnant llamas (143 mm Hg data from literature). The fall in HR when raising the head is a reflex mediated by efferent cholinergic pathways, probably vagal and generated in baroreceptors. These cholinergic pathways do not play a role in the increase in MAP. The role of the adrenergic system in MAP increases observed when raising the head remains to be investigated. FONDECYT 89-1080.