A comprehensive comparative study of etacizin (an antiarrythmic drug) pharmacokinetics and cardiovascular effects was performed with participation of nine subjects in usual circumstances and during 7-d head-down tilt (HDT, -8 degrees). Drug concentration in blood plasma was determined by HPLC with the spectrophotometric method; the cardiovascular function was evaluated based on ECG, tachycardiography, and rheography. HDT was shown to markedly reduce maximal concentration of the drug. Analysis of the CV functional parameters during etacizin administration evidenced that it increased HR significantly as on the background of usual motor activities, so in HDT and elongated the PQ-interval only under the normal motor activity.