Lateral positions of the body have some effect on autonomic nervous system. Systemic peripheral resistance is the main determinant of after load to the heart. It is regulated by the arterioles via sympathetic nerves and directly affects the diastolic blood pressure. One hundred asymptomatic healthy male subjects, aged 17-23 years, participated voluntarily in the present study, undertaken, to assess the effect of lateral positions of body on systemic peripheral resistance and other cardiovascular parameters. Cardiovascular parameters were recorded by mercury sphygmomanometer and Impedance Cardiovasograph (Nivomon) in three positions supine, left lateral and right lateral decubitus. Results showed significant increase in systemic peripheral resistance, systemic peripheral resistance index, and diastolic blood pressure in left lateral position. All the parameters were significant decreased in right lateral decubitus position in comparison to supine. Systemic peripheral resistance was maximum in left lateral position which indicates maximum sympathetic activity in left lateral position among the three positions supine, left lateral and right lateral decubitus. So, one should avoid left lateral decubitus position during rest to avoid extra load on the heart.