A client with unstable angina and chronic kidney disease is receiving a continuous infusion of unfractionated heparin based on a heparin drip protocol.  Which value for activated partial thromboplastin time (aPTT) would indicate to the nurse that the heparin therapy is at an optimal therapeutic level?

1.  35 seconds
2.  40 seconds
3.  60 seconds
4.  85 seconds