Regression of left ventricular dilation and hypertrophy after removal of volume overload. Morphological and ultrastructural study.

Gross and ultrastructural changes occurring in the left ventricle in response to chronic volume overload were studied in dogs. One group of dogs was examined 28-43 days after an aortocaval fistula had been created; congestive heart failure had developed at the time of the examination. Two other groups of dogs were investigated 78 ± 17 (SD) days and 178 ± 4 days after similar fistulas had been closed. A group of control dogs was also studied. Aortocaval fistulas produced significant left ventricular dilation and hypertrophy. Ultrastructural changes included enlargement and distortion of intercalated disks, increase in number but decrease in size and relative volume of mitochondria, and loss of lateral alignment of sarcomeres. Left ventricles, 78 days after the fistulas had been closed, were not different ultrastructurally or grossly from those in dogs with patent fistulas. After 178 days of closure, ventricular mass and volume had decreased; mass was still significantly greater than that in normal dogs, but cavity volume was not. Ultrastructural abnormalities in dogs after 178 days of closure were much less marked than those in dogs with patent fistulas, and ultrastructure was hardly distinguishable from normal. The findings in these experiments indicate that gross and ultrastructural abnormalities produced in the left ventricle by chronic volume overload are largely, if not completely, reversible.