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Figure 4 Peak positive LV dP/dt (LV dP/dtmax; expressed as a percentage of baseline values) during isoproterenol infusion in adult, middle-aged and old rabbits. Results of two-way analysis of variance: p < 0.01 for age; p < 0.01 for dose; and p < 0.01 for age x dose. 
p < 0.01 versus adults; 
p < 0.01 versus baseline. Solid bars = adult rabbits; striped bars = middle-aged rabbits; open bars = old rabbits.