5-cis Carbaprostacyclin is a stable analog of PGI2 and an isomer of carbaprostacyclin. It is a weak inhibitor of human platelet aggregation with an IC50 of 2.8 μM compared to 0.3 μM for carbaprostacyclin.{509,3320} 5-cis Carbaprostacyclin is a much weaker effector of rabbit mesenteric artery relaxation with an EC50 of 104 μM compared to 5.9 μM for carbaprostacyclin. It even antagonizes the adenylate cyclase activation induced by carbaprostacyclin.{3320}