A descriptive study was conducted to test the null hypothesis: There will be no statistically significant difference between serum activated partial thromboplastin time (aPTT) obtained by two methods; venipuncture and large bore femoral arterial catheter. The convenience sample consisted of seventeen adults who had undergone percutaneous transluminal coronary angioplasty (PTCA) for the treatment of coronary artery disease. After the PTCA procedure, patients returned to an intensive care unit with a femoral intra-arterial catheter in place. Seventeen pairs of serum samples were obtained; one by venipuncture and one through the femoral intra-arterial catheter. Prior to obtaining the sample from the femoral intra-arterial catheter, 6.0 milliliters (3 times the deadspace of the catheter) of blood was withdrawn and discarded. aPTT samples were analyzed. T-tests were used to compare the results. Findings revealed that there was no statistically significant difference in the aPTT value when drawn from venipuncture versus the femoral intra-arterial catheter.