Plasma heparin neutralizing activity in patients with valvular stenosis and prosthetic heart valves.

Patients with mitral and aortic valvular stenosis had plasma heparin neutralizing activity (HNA) which were comparable to the control group. In contrast, plasma HNA was elevated in patients with prosthetic valves, particularly in the group with prosthetic aortic valves. Neither the type nor the size of the valve appeared to influence the HNA level. No correlation was evident between plasma HNA levels and a history of systemic arterial embolism. It remains to be determined whether elevated plasma HNA levels result from platelet aggregation on the valve surface, or from platelet lysis due to turbulence around the prosthetic valve.