The clinical diagnosis of major infarction resulting from coronary insufficiency or occlusion is usually reliable, especially when confirmed by the presence of suitable electrocardiographic changes, slight fever, leukocytosis and an increased sedimentation rate.1However, there are some cases in which the clinical diagnosis is in doubt and in which additional data are desirable or essential for confirmation. Such cases include those with (a) an indefinite or atypical history, with or without positive electrocardiographic findings, (b) a definite history but negative or inconclusive electrocardiographic findings and (c) nodefinite history but apparently positive electrocardiographic findings. Infarction in the " acute" stage is essentially a problem for clinical diagnosis; the patient can rarely be moved for roentgen studies and the electrocardiogram is usually positive. Infarction in the healing or "healed" phase is often a problem for joint clinical and roentgen examination; the electrocardiogram has not infrequently reverted to normal or become nondiagnostic. It