The authors used a multi-dimensional approach to the study of the effects of intra-operative myocardial protection; the results of three series of investigations are reported. First, conditions underlying the effectiveness of the authors' modified cardioplegic solution were studied by laboratory and histological methods in ex vivo guinea pig hearts. Evidence is presented for the detrimental effects of catecholamines and the beneficial action of inosine. The second part of the report deals with problems of effective myocardial cooling in partially ischaemic canine hearts, investigated by infrared thermographic examinations of temporal and spatial thermal distribution over the entire visible cardiac surface. At last the authors present the result of their complex intra- and postoperative enzyme analysis combined with mathematical evaluation (cluster analysis in a group of patients suffering from ischaemic heart disease).