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1. In experiments on closed chest dogs in a control group and a group of previous isovolaemic haemodiluted dogs a cardiovascular stress was produced by means of reduction of inspiratory O2 content to 6% O2--2. Under haemodilution only small changes of the heart rate, aortic pressure and dp/dtmax occurred, pointing to a decreased sympathoadrenergic response. Augmentation of LVEDP and pulmonary artery pressure is considered to be related to left ventricular insufficiency.--3. According to haemodynamic changes myocardial O2 demand in the control group during hypoxia is increasedby 120% and in contrast remains unchanged after previous haemodilution.--4. Despite the reduced oxygen content under haemodilution severe arterial hypoxemia affects mean survival time of the animals (18.5 min and 21.5 min respectively) only little. However, there is a greater variation from 11 to 26 min in the haemodiluted animals.

1. In experiments on 5 closed chest dogs an isovolaemic haemodilution with 6% dextran resulted in a drop of haemoglobin content to 6,4g%. Except for a small decrease of arterial pO2 and O2-saturation the body oxygen supply remained undisturbed. -- 2. According to only very small haemodynamic alterations (except compensatory cardiac output increase) myocardial O2-demand increased very little and mainly is caused by moderate augmentation of ventricular wall tension. The decrease of arterial O2 content was fully compensated by an increase of myocardial blood flow. O2 supply to the myocardium was not critically changed. -- 3. In accordance with other investigators it is concluded that in case of coronary insufficiency or increased myocardial O2 demand intentional hemodilution should be avoided. Patients with myocardial insufficiency considered for therapeutic hemodilution should be digitalized preoperatively.