A 67-year-old mand in whom mitral and tricuspid Bjork-Shiley tilting disc prostheses had been implanted 68 months previously presented with thrombotic obstruction of his tricuspid prosthesis. Initial cardiac catheterization demonstrated a significant transprosthetic tricuspid diastolic gradient (9.5 mmHg) with a calculated prosthetic valve orifice area (0.62 cm2) indicating a critical degree of stenosis. The resting cardiac index was markedly reduced (1.5 l/m2/min). Following an intravenous infusion of streptokinase for 66 hours, repeat cardiac catheterization revealed a 50% reduction in transprosthetic diastolic gradient across the tricuspid valve (4.7 mmHg), a greater than fourfold increase in prosthetic valve orifice area (2.87 cm2) with a normal resting cardiac index (3.1 l/m2/min).