1. The purpose of this study was to determine whether events early in systole, a period which may be more descriptive of ventricular performance than the average of events in systole, can be determined by multiple gated radionuclide cardiac blood pool imaging.

2. We examined 16 ventricular volume curves, using a digital filtering method in the frequency domain to smooth statistical noise. Ejection fraction was unchanged by such filtering but the peak rate of change of volume during systole was greatly affected by different bandwidths. Therefore we derived an index, the mean ejection time, which is influenced by changes in the shape of the systolic portion of the volume curve but is unchanged when measured from curves treated by different filter bandwidths.

3. We infused isoprenaline (2 μg/min; eight patients), atropine (1.2 mg; eight patients) or dobutamine (360 μg/min; six patients).

4. Isoprenaline and atropine caused a similar increase in heart rate (isoprenaline + 27 beats/min; atropine + 20 beats/min) but after dobutamine there was little change in heart rate (+4 beats/min). After isoprenaline and dobutamine ejection fraction increased (0.51 ± sem 0.04 control; 0.73 ± 0.04 after isoprenaline; 0.53 ± 0.03 control; 0.65 ± 0.06 after dobutamine) but was unchanged by atropine (0.46 ± 0.07 control; 0.48 ± 0.07 after atropine).

5. The mean ejection time decreased by 55 ms after isoprenaline, by 49 ms after dobutamine but by only 14 ms after atropine. Changes in peak rate of change of volume in systole were more variable.

6. Radionuclide gated blood pool studies can be used to study the effects of pharmacological intervention on events in early systole and the variable ‘mean ejection time’ is independent of curve-fitting techniques.

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