O DETERMINE whether, in certain aspects, hypertrophied heart muscle behaves differently from normal heart muscle simple observations were performed. Papillary muscle strips from the left ventricle of rats, the hearts of which had been caused to hypertrophy, were compared with papillary strips from normal rat hearts by measuring tension developed at various weights in a perfused isolated muscle strip preparation. Having parallel muscle fibers and sharing in hypertrophy of the left ventricle, 1 -2 papillary muscle is well suited to studies of isometric contraction.Methods Hypertrophy of the left ventricle was achieved by the method of Hajdu and Beznak.3 Silver rings of an internal diameter of 1.50 mm. were snugly placed about the ascending aorta of male rats between the ages of 30 and 90 days weighing 150 to 250 Gm. Blue Spruce Farm Sprague-Dawley rats were used for operation and for control animals. Between 21 and 90 days after placement of the ring, the rat hearts were tested. Animals failing to gain weight normally were discarded. The animal was weighed, given ether anesthesia, and the heart quickly removed. Following the method of Hoffman and Kelly, 4 the actively beating fresh heart was transferred to oxygenated Tyrode's solution, the left ventricle opened, and a papillary muscle, gently handled, was tied at its apex with 0000 silk and excised at its base. The muscle was inserted into a plastic muscle holder and its base firmly pressed against two pin-point platinum stimulating electrodes. The strip was then placed Prom the Medical Service, Veterans Administration Hospital, and the Department of Medicine, State University of New York, Upstate Medical Center, Syracuse, jSTew York.Supported in part by grants from Xew York Heart Assembly and Heart. Association of Onondaga County.Drs. Giambattista and Winterberger were recipients of student research fellowships during the summers of 1958 and 1959.Received for publication August 5, 1960. in a muscle warmer and perfused at a rate of 3 ml./min. with Tyrode's solution (XaCl, 142 niM/ L.; KCL, 2.7; dextrose, 5.5; XaHCO 3 , 12.5; MgClo, 0.5; XaH 2 PO 4 , 3.7). A mixture of 95 per cent O 2 and 5 per cent CO 2 was delivered through a sintered disk at the bottom of the muscle warmer at a rate of 6 ml./min. The muscle warmer was surrounded by a constant temperature bath kept at 27 C. The suture from the apex was attached vertically to a horizontally placed Grass force displacement transducer (Model FT 0.03). Gram weights were used to calibrate the displacement of the transducer which was connected through a preamplifier to a channel of a Grass recorder. A micrometer screw adjustment was used to tighten the suture and the muscle was placed under 1 Gm. of tension. The preparation was then left in the muscle bath for one hour before stimulation. A Grass stimulator (Model S4C) and isolation unit were used. The muscle was stimulated at 5-second intervals with a rectilinear pulse of 10-msec. duration. Voltage was increased until a maximum response was evoked. Resting tension ...
