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Figure 4 Effects of 1 µmol/l desipramine (DMI) on the positive inotropic effect of noradrenaline (in the presence of 1 µmol/l phentolamine) in right atrial (RA) trabecular strips obtained from 5 children in group A (A, left panel) (3 males and 2 females; mean age 9 ± 4 years) and from 7 elderly patients in group B (B, right panel) (5 males and 2 females; mean age 60 ± 3 years) (New York Heart Association functional class 1.71 ± 0.18). Ordinates: positive inotropic effect in percent maximal response; abscissa: molar concentrations of noradrenaline. The basal force of contraction was 2.5 ± 0.4 mN (without DMI) and 5.0 ± 0.8 mN (with DMI) in group A and 3.6 ± 0.6 mN (without DMI) and 4.2 ± 1.3 mN (with DMI) in group B. The maximal force of contraction was 7.2 ± 0.6 mN (without DMI) and 6.7 ± 1.0 mN (with DMI) in group A and 8.7 ± 0.7 mN (without DMI) and 6.1 ± 1.3 mN (with DMI) in group B. Data are presented as the mean value ± SEM.