Cardiac metastasis should be strongly suspected in the cancer patient with sudden onset of unexplained tachycardia, arrhythmia, or congestive heart failure. Conduction defects and low voltage on electrocardiographic examination and an enlarged heart shadow on the chest film are virtually confirmatory. Thirty-eight such patients were treated through anterior and posterior opposing portals and received 2,500-3,500 rads in 3-4 weeks, except for 6 lymphoma and leukemia patients who were controlled with lower doses (1,500-2,000 rads in 11/2-2 weeks). Primary sites and duration of improvement were as follows: breast (11/16 patients): 2-36 months; lung (2/7 patients): 1-9 months; lymphoma and leukemia (6/7 patients): 2-4 months; others (4/8 patients): 1-4 months. Overall, the clinical improvement rate was 60%, with durations of 12 to 36 months.