Simultaneous M-mode echocardiograms and phonocardiograms were recorded in 19 patients with chronic Chagas' disease, and were digitised and compared with normal in order to study systolic and diastolic left ventricular function. Five of the patients were in New York Heart Association class 1, 9 in class 2, and 5 in class 3. Left ventricular cavity dimensions were increased in 3 and shortening fraction reduced in 1. Peak velocity of circumferential fibre shortening was below the 95% confidence limit of normal in 9. In contrast to previous echocardiographic studies, diastolic abnormalities were common, with prolongation of isovolumic relaxation time in 9 patients and reduced rate of dimension increase in 11. However, in spite of regional disease, documented angiographically in 5 of 6 patients, there was no evidence of asynchronous wall motion during relaxation seen in patients with coronary artery disease and comparable segmental abnormalities of wall motion. The relative timing of aortic valve closure and minimum cavity dimension was normal in all but 3 patients, and a significant dimension change during isovolumic relaxation in only one. Thus diastolic disturbances are common at all stages of Chagas' disease, and may represent a fundamental aspect of the pathological process as it affects the left ventricle.