A low myocardial content of alpha-ketoglutarate during heart surgery might aggravate ischaemic injury. 24 men undergoing coronary surgery participated in a randomised controlled study. 28 g alpha-ketoglutarate was added to blood cardioplegia for intermittent antegrade intracoronary perfusion in 13 cases. alpha-ketoglutarate reduced the appearance in blood of the ischaemic markers creatine kinase MB and troponin T (at 4 h after release of aortic cross-clamp; median [95% CI] 49 [37-60] micrograms/L in controls vs 32 [27-37] micrograms/L for creatine kinase MB, 2.0 [1.2-2.8] vs 1.1 [0.8-1.4] micrograms/L for troponin T). These findings signify attenuated ischaemic injury, possibly secondary to enhanced myocardial oxidative capacity.