Analysis of the cardiac output during Valsalva maneuver and passive leg raising in order to perform a clinical study. To do the measures the qCO (Quantium Medical, Mataró, Spain) has been used, a medical device that measures the cardiac output non-invasively by bioimpedance. The test to be performed is defined using a protocol that determines the duration of the measures and how to perform it. The registers were performed to healthy volunteers. A statistical study has been done to find differences between the different states of the test and differences between characteristic groups of volunteers; sex, sport or smokers.