The criteria of Msc-positivity were: typical accumulation of hot spots in 2 directions of planar scan in the 24-48-hr measurements, while in atypical cases the hot spots were present only in the 48 hr picture. Twenty-one male volunteers were assessed. 18 of them had ACM (2 patients were studied repeatedly). The negative and positive control cases exhibited the expected Msc pattern. Seven ACM patients were regarded typically positive, in 5 cases atypical positivity was stated, and 6 patients were classified as Msc negatives. The heart lung activity ratio was 1.75 +/- 0.45 and 1.68 +/- 0.44 for typical and atypical positive cases, respectively. The control and DCM H/L ratios were 1.15 and 1.3 +/- 0.2, respectively, in AMI the H/L was 1.91, in DCM of dilatative phase it was 1.55 +/- 0.06 with serum myosin in the normal range. Heart dilation in the DCM groups: 5 dilated out of 7 typically positive cases while in atypically positive, and negative cases the dilation occurred in 2 out of 5 and 1 out of 6 cases, respectively. Low LV-EF (less than 45%) were found in ratios of 4/7, 2/5, and 1/6 in typically positive, atypically positive and negative cases, respectively. Elevated PCP similar ratios. In the same groups pathological ECG was seen in ratios of 5/7, 1/5, and 1/6, respectively. The g-GT activity was enhanced in all cases, there was, however, no evident correlation between the actual enzyme activity and intensity of hot accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)