The linear dimensions of the ventricle of an in situ perfused trout heart were measured with an ultrasound scanner. Using a pyramidal model, linear dimensions taken from real-time, two-dimensional, echotomographic images of the ventricle were used to calculate ventricular end-diastolic and end-systolic volumes and, by the difference between them, stroke volumes for various filling and output pressures. Stroke volumes calculated from the ultrasound measurements were significantly correlated with actual stroke volumes determined from cardiac output and heart rate and had a regression line slope close to one. Increases in stroke volume with greater filling pressures resulted from increased ventricular end-diastolic volume with constant end-systolic volume; end-systolic volumes were negligible. Maintenance of stroke volume with increasing output pressure was by increases in both end-diastolic and end-systolic volumes. Decreases in stroke volume with very high output pressures may result from convergence of end-systolic and end-diastolic volumes.

This content is only available via PDF.