Two-dimensional echocardiography and indium 111-labelled platelet scintigraphy have proved helpful in the diagnosis of left intraventricular thrombosis. In this study, both methods were used to investigate the time-related changes undergone by such thrombi in 30 patients (26 with myocardial infarction, 4 with dilated cardiomyopathy) who presented with left intraventricular thrombosis diagnosed by echocardiography and systematically explored by indium scintigraphy. These 30 patients were divided into 2 groups depending on whether the initial scintigraphy was positive (group I, 19 patients) or negative (group II, 11 patients). The follow-up (mean 21.6 months) was clinical and paraclinical, with control echocardiography repeated at 1.5 and 8.5 months in both groups and control scintigraphy at 1.5 month in group I patients. At the 1.5 month echocardiography, the intraventricular thrombosis persisted in 14/16 examinations in group I patients and in only 2/10 examinations in group II patients (p less than 0.01). At the 1.5 month scintigraphy, performed in 16/19 group I patients, this examination had become negative in 8 cases, whereas the 2D-echocardiography remained positive. During the follow-up period 4 patients in group I had an embolic accident, as against none of the group II patients (p less than 0.01); 3 of these 4 patients had persistent uptake at control scintigraphy. At echocardiography, only a protrusion image seemed to be predictive, as it was present in 3 of 4 patients with embolic accident.(ABSTRACT TRUNCATED AT 250 WORDS)