International societies that sponsor scientific meetings, research grants and other activities in this field:

Attending scientific meetings and presenting your work at them is not only important for sharing new information among scientists; it is also an essential part of a scientist's career development. B. Fischer & M. Zigmond at the University of Pittsburgh have put together a useful guide (in PDF format) for how to attend such meetings and present your work at them.

• International Society on Thrombosis and Haemostasis (ISTH)
  ISTH sponsors an important international meeting on thrombosis and hemostasis every two years (on odd numbered years). The next meeting will be the XXII^nd ISTH Congress in Boston, MA, USA, on July 11-16, 2009, with an abstract deadline of January 31, 2009. The ISTH also sponsors an annual meeting of the official ISTH committees and working groups comprising the Scientific and Standardization Committee (SSC): The 54^th Annual SSC Meeting will be held in Vienna, Austria on July 2-5, 2008.
  
  
• American Society of Hematology (ASH)
  ASH holds a large scientific meeting every December, which covers all aspects of hematology (including blood clotting and vascular biology). The abstract deadline is usually sometime in August.
  
  
• Gordon Research Conferences
  This organization sponsors a series of small summer conferences in rural New England, including an important meeting on Hemostasis that is held during the summer of even numbered years. Other topics of interest include Vascular Cell Biology, and Proteolytic Enzymes and their Inibitors. They also sponsor some winter conferences at other venues. The conferences are five days long and each subject is generally offered every other year. Because Gordon Conferences are small and located in relatively isolated areas, they are excellent opportunities to meet and talk with your colleagues. This can be especially valuable for students, postdoctoral fellows, and those new to an area of investigation. Attendance is limited, so be sure to apply early.
  
  
• American Heart Association (AHA)
  The AHA holds a very large scientific meeting every November, devoted mostly to cardiology. The AHA's Council on Arteriosclerosis, Thrombosis and Vascular Biology (ATVB) sponsors a smaller meeting each spring of interest to researchers working on atherosclerosis, thrombosis and vascular biology. The AHA also funds research grants related to heart disease and stroke (in a broadly defined way) in the United States.