1. Guinea-pig ventricle was used in the RNase protection assays to determine which α-isoforms of the Na+-K+ pumps are present, and ventricular myocytes were used in whole cell patch clamp studies to investigate the actions of α- and β-adrenergic agonists on Na+-K+ pump current. 2. RNase protection assays showed that two isoforms of the α-subunit of the Na+-K+-ATPase are present in guinea-pig ventricle. The mRNA for the α1-isoform comprises 82% of the total pump message, the rest being the α2-isoform. 3. We have previously shown that β-adrenergic agonists affect Na+-K+ pump current (I(p) through a protein kinase A (PKA)-dependent pathway. We now show that these β-effects are targeted to the α1-isoform of the Na+-K+ pumps. 4. We have also previously shown that α-adrenergic agonists increase I(p) through a protein kinase C (PKC)-dependent pathway. We now show that these α-isoform effects are targeted to the α2-isoform of the Na+-K+ pumps. 5. These results suggest the effects of adrenergic activation on N+-K+ pump activity in the heart can be regionally specific, depending on which α-isoform of the Na+-K+ pump is expressed.