Caloxin 1C2 is a specific PMCA (plasma-membrane Ca 2+ -ATPases) inhibitor. Caloxin 1C2 is selective for PMCA4 over PMCA1, 2 and 3. The K i values of Caloxin 1C2 are 2.3 μM for PMCA4 and 21 μM for PMCA1. Caloxin 1C2 dose not cause any significant effects on total Ca 2+ transfer. Caloxin 1C2 affects coronary contractility.