Hypotension was induced on 15 dogs by intravenous injection of hexamethonium bromide (C(6)) following intravenous pentothal anesthesia. The following alterations in E. C. G. were noticed. (1) R-R: R-R interval showed shortening or prolongation or no change. These changes occurred in frequency of 3:1:1 as in order. Tachycardia developed in all cases, even in dogs where no changes in blood pressure were produced with C(6). (2) Impairment of conduction: No marked changes were seen in P-Q and Q-T intervals. (3) QRS: R wave was depressed at the level of 80 mm HG of systolic blood pressure and returned to normal with recovery of blood pressure. Neither low voltage nor widening of QRS were observed in the case where systolic blood pressure remained over 60 mm HG. (4) P: Slight elevation of P waves were noticed in leads II and III. (5) T: Prolongation of T wave was seen in two, low and diphasic T in six, inverted T in three and there was seen no change in T wave in four dogs. These alterations returned to normal with recovery of blood pressure. (6) ST: Depression of ST segments was noticed in six of 15 dogs where systolic blood pressure was lowered than 70 mm HG. (7) Abnormal stimulus formation. One of 15 dogs died of ventricular fibrillation followed marked hypotension which developed after posture change. One another dog developed temporary ventricular fibrillation.