Myocardial Tension and Oxygen Uptake.

• Since the report of Evans and Matsuoka ' a half century ago, it has been known that myocardial oxygen uptake increases in approximately a linear fashion with mean arterial pressure, but is affected only slightly by increases in cardiac output.' This paradox, that "pressure work" is much more costly than "volume work," complicated the analysis of the energetics of myocardial contraction. A consideration of the changes in mechani-