Rabbits, ages 4-24 weeks, were injected with saline or thyroxine (150 micrograms/kg) for 7 days, and force-velocity curves were generated using papillary muscles from these hearts by a method described previously. In addition, the structure and relative amounts of myosin isozymes from papillary muscles and from 3- to 5-mg segments of the left and right ventricular free wall were analyzed by pol...
