Of 70 consecutive cancer patients referred from radiotherapy for bone scans, 32% showed cardiac uptake of 99mTc-(Sn)-pyrophosphate; only 9% of a control group showed this uptake. Of those with prior left hemithorax irradiation, 60% showed cardiac uptake; only 12% of those with irradiation elsewhere showed this phenomenon (p less than .01). The patients who had no increased uptake tended to have shorter irradiation-to-scan time intervals (less than 10 months) than those who did show increased uptake (mean of 22 months).