Figure 2. Effect of frequency of stimulation (0.5-2 Hz) on isometric force of contraction in electrically driven papillary muscle strips from nonfailing (7 preparations of 5 hearts) and failing (12 preparations of 8 hearts) human myocardium. Asterisks denote significance vs. 0.5 Hz (P < 0.05). Abscissa = frequency of stimulation (Hz); ordinate = change in force of contraction (mN).