Myocardial performance in the newborn lamb

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Abstract
We compared myocardial performance in newborn lambs over the first 3 wk of life with that of ewes. Heart rate was higher in newborn lambs than in ewes. The ratio of left ventricular preejection period to left ventricular ejection time was similar for newborns (0.31 +/- 0.02) and ewes (0.31 +/- 0.01). Cardiac output in ml/min per kg body weight in the newborn was 397 +/- 55 at 1 wk, 314 +/- 30 at 2 wk, and 274 +/- 10 at 3 wk, compared to 125 +/- 8 in ewes. Stroke work was comparable in both age groups. Left ventricular dP/dtmax averaged 3,723 mmHg/s in lambs compared to a mean value of 2,257 in ewes. These studies establish that the myocardium of newborn sheep contracts vigorously in vivo and equals or exceeds the level of performance of the myocardium of adult sheep, as estimated by a variety of indices of myocardial function.