Two experimental studies of cardiovascular reactivity are presented, based on the sensitivity of the measuring conditions and on its fiability. In the first study, a 89 student sample was engaged. The registered physiologic variables were the interbeat interval (R-R), pulse transit time from the peak of the electrocardiogram R wave to the radial artery and the electrodermic activity. In the experimental procedure registrations in base line conditions, relax base line, electric shock avoidance and inescapable noise were included. Data showed a high covariation between the interbeat interval and pulse transit time to the radial artery, producing a great decrease in the active coping task compared to the passive coping task; these two physiologic indexes were the most sensible in the evaluation of cardiovascular reactivity. In the second study the engaged sample consisted of 20 individuals, divided into two groups according to their reactivity values. The registered physiologic variables were the heart rate, pulse transit time from the peak of the electrocardiogram R wave to the radial artery and the electrodermic activity. The experimental registration procedure in base line conditions, relax base line and electric shock avoidance in two measured sessions (test and retest) separated by an interval in time of six months. The comparison between the relax base line situation and the shock avoidance task, showed a significative difference in the pulse transit time index in the most reactive group of individuals, both in the test and in the retest. The group of less reactive individuals did not present significative difference in anyone of the two sessions. The heart rate didn't present significative difference in any group and any session.