The inotropic action of paired pulse stimulation in the normal and failing heart: an experimental study.

Fixed rate single and paired pulse stimulation has been compared in the normal dog left ventricle and in the left ventricle failing after myocardial damage. In the normal heart a persistent positive inotropic effect occurred, seen mainly as an increase in rate of rise of left ventricular pressure, rather than total work. In the failing heart there was a transient positive inotropic effect, followed by increasing ventricular failure. The increasing failure was reversed by a return to single pulse stimulation.