Abstract: An oligosaccharide containing about 20 monosaccharide units is provided. This oligosaccharide designated (M.sub.9 G).sub.2 is a copolymer .beta.-D-(1.fwdarw.4) connected mannuronopyranose units and an .alpha.-L-(1.fwdarw.4) connected guluronic acid unit at a ratio of 9:1. In addition, 40-60% of the carboxylic functional groups are esterified with propanol, 2-propanol or methanol, and substantially all of the C.sub.2 carbons and about 50% of the C.sub.3 positions of the residues are sulfated, such that the resulting compound contains about 7-13% organic sulfur. The compounds are used for the prevention and therapy of thrombosis-induced ischemic vascular diseases of the heart and the central nervous system, for treating acute thrombosis-induced brain infarction and in coronary ischemia-induced angina, and for treating hyperlipoproteinemia and lowering the relative amount of cholesterol.