A microcatheter (100) for delivery of embolic fluids includes an outer member (102) dimensioned for insertion within a blood vessel adjacent an embolization site. The outer member defines a first longitudinal lumen (120), and an inner member (104) is selectively positionable within the first longitudinal lumen of the outer member. The inner member defines a second longitudinal lumen (132) and has a delivery port (176) in fluid communication with the second longitudinal lumen for passage and delivery of embolic fluids toward the embolization site. A valve (140) is disposed within the outer member. The valve is dimensioned to establish a substantial seal about the inner member, to minimize entry of the embolic fluids within the first longitudinal lumen of the outer member subsequent to delivery thereof toward the embolization site.
