Phagosonography of 100 normal subjects and 100 patients with cardiac cancer (CC) is described. The apparatus was self-designed and self-manufactured. The pre-ejection period and other 8 quantitative indexes in PSG were compared and abnormal level existed in patients with CC (P less than 0.01). The phagosonograms drawn in 54 patients with esophageal, cardiac or gastric benign diseases served as control. The diagnostic accuracy of PSG was 97% positive, 3% suspicious in CC and 100% negative in the normal subjects. It was 3.7% suspicious in the esophageal, cardiac or gastric diseases. PSG is very important in the early diagnosis of CC and is also of value in the prediction of a successful operation. The authors believe that PSG can reflect the changes in cardiac and esophageal motor function. In CC, the PSG changes are mainly due to the malfunction in the dilation and contraction of the lower esophageal sphincter. This malfunction shows itself earlier than the pathomorphology and provides a basis for the early diagnosis of CC. Phagosonography is a new method in the research on the motor function of the sound producing viscera, the diagnosis of their diseases and the observation of the treatment result. Being able to be performed with the patients in physiological and non-invasive state, it is suitable for screening.