The purpose of this proposed research is to investigate the effects of respiration, including various modes of assisted respiration, on the performance of the left ventricle. Utilizing chronically implanted endocardial sonomicrometer crystals, and angiographic studies, we plan to: (1) develop and validate left ventricular volume measurements in a chronic dog preparation with the aim of producing serial measurements of LV volumes and LV free-wall thickness, (2) develop an acceptable system for measurement of ventricular surface pressure, and (3) using the above techniques, to define the effects of spontaneous and variously assisted respiration on LV performance in terms of contractility, preload, afterload and diastolic compliance/viscoelastic properties.