We have designed and tested two amplification circuits for measuring HL-1 cardiac action potentials, single-ended and differential. We describe the improvements in performance resulting from the differential configuration. These improvements are especially important considering the cell culture's aqueous environment that experiences DC drift. In addition we have designed and fabricated a 4X4 gold microelectrode array and cultured HL-1 cells on the electrodes. The array is connected to our circuit through a custom made Pogo pin jig to allow for easy measurements from the electrodes while cells are being cultured. This setup allowed us to obtain initial results for modeling the transfer function of the cell culture as a passive device network. Testing has confirmed the circuits are capable of filtering low frequency signals including DC drift and frequencies above 5 kHz. The amplification was achieved through two gain stages with a total gain of 60 dB for the single-ended and 46 dB for the differential circuits.