When the auricles fibrillate, the following effects are observed.
1. The arterial blood pressure may rise, fall, or remain stationary. Usually it falls. If it falls, it generally rises again towards or to the initial pressure.
2. The venous pressure changes are the reverse of the arterial.
3. The intestinal volume and the cardiac output changes are in the same direction as those of arterial blood pressure.
4. From these observations it may be concluded that the peripheral circulatory effects are purely passive.
5. The volume of the heart decreases except in instances where there is reason to believe that the circulation is failing.
All the changes described in the foregoing paragraphs, and also the variations in blood pressure reactions which occur from time to time, are attributable to alterations in the rate of ventricular contraction. Similar, though perhaps less profound changes, are seen when the heart rate accelerates in like degree in response to regular induction shocks.