whole blood versus plasma measurements of glutamate and alanine across the human myocardium comparison of whole blood and plasma aortocoronary sinus concentration differences of glutamate and alanine were made before during and after coronary sinus pacing in seven patients with normal and six patients with stenotic coronary arteries mean differences between duplicate analyses were greater in whole blood than plasma both of glutamate 75 58 vs 33 30 mumoll p less than 0001 and of alanine 79 70 vs 38 34 mumoll p less than 0001 concentrations of glutamate were 34 and of alanine 14 times higher in whole blood than in plasma blood cells were calculated to be responsible for about 20 of glutamate and alanine blood exchanges across the heart plasma and whole blood fluxes were closely positively correlated glutamater 081 alaniner 088 and had always the same direction differences in myocardial exchanges of amino acids between the patients with and without coronary artery disease as well as rapid changes during pacing could be demonstrated in plasma analyses but were not significantly reflected in whole blood glutamate determinations this seemed to be due to the greater variations in whole blood analysis in conclusion differences in aortocoronary sinus plasma concentrations reflected although underestimated whole blood fluxes because of considerable gains in precision of analysis plasma should be preferred to whole blood for evaluations of glutamate and alanine exchanges across the human heart