Pressure-volume relationships in the left atria of anaesthetized dogs

1. Pressure-volume relationships of the left atria were studied in thoracotomized dogs anaesthetized with sodium pentobarbitone and ventilated artificially. Controlled volumes of saline were injected into the left atrium using a method by which the injections were triggered by the R wave of the normal ECG, during the period of the V wave of the left atrial pressure waveform. 2. The change in the amplitude of the V wave was found to be linearly related to the injected volume. Similar observations made while the pulmonary artery was occluded revealed that this linearity in the pressure-volume relationship of the atrium extended down to small volumes.