Pre-ablation impedance was evaluated for its ability to detect electrode-tissue contact and allow creation of long uniform linear lesions with a multielectrode ablation catheter. The study consisted of 2 parts, both of which used the in vivo pig thigh muscle model. In part 1, a 7 Fr. multi-electrode catheter was held in 3 electrode-tissue contact conditions: (1) non-contact; (2) light contact with a 30g downward force; and (3) tight contact with a 90g downward force. Impedances were measured in unipolar, modified unipolar and bipolar configurations using a source with frequencies from 100 Hz to 500 kHz. Compared with noncontact, the impedance increased 35±22% with 30g contact pressure and 68±40 % when the contact pressure was increased to 90 g across the range of frequencies studied. In part 2, the same catheter was held against the tissue with different forces. Pre-ablation impedance was measured using a 10kHz current. Phased radiofrequency energy was applied to the 5 electrodes simultaneously using 10 W power at each electrode for 120s. A total of 32 linear lesions were created. The lesion dimensions correlated with preablation impedance. A unipolar impedance ≥190Ω indicates 95 % possibility to create a uniform linear lesion of at least 3 mm depth with our ablation system. We conclude that pre-ablation impedance may be a useful indicator for predicting electrode-tissue contact and the ability to create a continuous and transmural linear lesion with a multi-electrode catheter.