1. Pacing-induced heart failure was studied in eight dogs. Heart failure was induced by right ventricular pacing at 250–260 beats/min for 6 weeks. Evidence of heart failure was determined clinically and by measurement of left ventricular (LV) dimensions by transoesophageal echocardiography.

2. Haemodynamic measurements of LV pressure, maximum rate of rise of LV pressure (LVdP/dtmax), cardiac output, mean arterial pressure, heart rate, pulmonary artery and pulmonary wedge pressures were made during infusion of solvent (control) and the calcium sensitizer EMD 57033 (0.6 mg min−1 kg−1).

3. The degree of heart failure varied from mild to severe in different individuals, but in each case EMD 57033 exerted a positive inotropic effect on LV haemodynamics and dimension.

4. The positive inotropic effect of the calcium sensitizer was manifest by increased peak LVdP/dt with a subsequent increase in cardiac output at the same mean arterial pressure.

5. This study clearly demonstrates that there is the potential for improvement of contractility of the failing myocardium of the intact mammal by an agent with a mechanism of action which does not involve an increase in intracellular calcium.

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