Highly viscous silicone masses comprising alkenyl-terminated polydiorganosiloxanes which may be cross-linked by addition

Addition crosslinkable organopolysiloxane compositions which cure to organopolysiloxane elastomers of high elongation at break and high tear resistance contain a high viscosity, alkenyl-terminated, and substantially pendant alkenyl group-free organopolysiloxane, an organopolysiloxane having pendant alkenyl groups and optionally alkenyl-terminal groups, an Si-H functional crosslinker, and a hydrosilylation catalyst.