Effects of L-dopa on myocardial contractile force: a reappraisal.

The apparent decrease in myocardial force of contraction observed after L-dopa, 10 mg/kg i.v., is artifactual since the maximum rate of left venticular isovolumic pressure rise (dP/dt) remains elevated. The apparent decrease is due to shrinkage in heart size secondary to venous "pooling". The decrease in contractile force parallels a decrease in cardiac output. A peripheral decarboxylase inhibitor and L-dopa produce a decrease in both contractile force and dP/dt. Strain gauge arch recordings may produce false-positive data during marked venous pooling.