Gap19 TFA, a peptide derived from nine amino acids of the Cx43 cytoplasmic loop (CL), is a potent and selective connexin 43 (Cx43) hemichannel blocker. Gap19 TFA inhibits hemichannels caused by preventing intramolecular interactions of the C-terminus (CT) with the CL. Gap19 TFA is not blocking GJ channels or Cx40/pannexin-1 hemichannels. Gap19 TFA has protective effects against myocardial.