Myocardial contusions of variable severity were experimentally produced by an air-driven piston or serrated clamp in 29 dogs. Two 99mTc-labeled bone-seeking agents (99mTc pyrophosphate and 99mTc tetracycline) were used with cardiac scintigraphy to determine the sensitivity of these agents in detecting different degrees of myocardial damage. Results showed that 99mTc tetracycline was not a suitable scanning agent. 99mTc pyrophosphate produced positive scans in cases of complete (or nearly complete) transmural myocardial necrosis. Positive cardiac scans in clinical myocardial contusion may indicate the severity of the lesions and have prognostic significance.