According to Powers et collaborators the hypothesis that intramyocardial vessels may be collapsed in artificially ventilated patient with added PEEP, could be arisen. So, myocardial ischemia may explain why in some of those ones there appear signs of left ventricular failure. To test whether this reasoning was correct we measured LVEDP in normal dogs submitted to increasing levels of PEEP up to 40 cm H2O. Our results seem to point towards the following conclusions: a) In normal dogs, Starling relation is not altered and remains within the same hypercontractility pattern. b) As PEEP increases, ventricular function remains within the same curve up to 30 cm H2O and jumps to a higher contractility curve at 40 cm H2O of PEEP. All of this would suggest that under our experimental conditions it does not seem reasonable to assume the existence of left ventricular failure due to PEEP influence.