Background: It has been shown that transient increase in left ventricular (LV) stiffness, assessed by Dopller derived early filling deceleration time (DT), occurs during first 24-48 h after myocardial infarction (MI), but returns to normal within several days.We have reported that hyperbaric oxygen treatment (HBO) has favorable impact on left ventricular systolic function in patients (pts) with-aeute MI treated with thrombolysis.However, there are no data on the effect of HBO on diastolic function after MI. Methods: To assess acute and short-term effects of HBO on LV chamber stiffness we studied 74 consecutive pts with first acute MI, who were randomized to treatment with HBO combined with streptokinase or streptokinase alone.After thrombolysis, pts in HBO group recived 100% oxygen at 2 ATA for 60 minutes in a hyperbaric chamber.All pts underwent two-domensional and Doppler echocardiography 1 (afterthrombolysis), 2, 3, 7, 21, and 42 days after MI. Results:Pts characteristics, including age, sex, risk factors, as well as adjunctive post-MI therapy, infarct location and baseline LV volumes and EF were similar between groups (p>0,05, for all).For both groups, DT decreased nonsignificantly from day 1 to day 3, and increased on day 7 (p<0,001,for both groups), increasing nonsignificantly subsequently.Pattern of changes of DT was similar in both groups (p>0,05, by MANOVA) (Figure). Conclusion: It appears that HBO does not affect LV chamber stiffness in patients with acute MI treated with thrombolysis.