A new thrombolytic drug, renokinase, was administered intravenously to 30 patients with macrofocal myocardial infarction (MI), admitted to hospital within early hours of its onset. Changes in the venous network of the heart were assessed, using continuous thermodilution, in the presence of thrombolytic treatment. Coronary venous flow was shown to increase by 20% and more in 17 patients, more than 30% in 15 patients, and more than 40% in 10. Low MI was associated with a significant increase of blood flow rate in the coronary sinus as well as other cardiac veins, while anterior MI was associated with flow rate increase in the coronary sinus only. A 20-30% increase in any of the coronary flow parameters limited the necrosis focus, as evidenced by precordial mapping from 35 ECG leads. Renokinase (60,000 units) was well tolerated by the patients.