Fifty-nine patients ( 6314 years ) with acute main or lower lobe pulmonary embolism and echocardiographic RV to left ventricular dimension ( RV/LV ) ratio 1.0 were randomized to receive unfractionated heparin and an USAT regimen of 10 to 20 mg recombinant tissue plasminogen activator over 15 hours ( n = 30 ; USAT group ) or unfractionated heparin alone ( n = 29 ; heparin group ) .