Patient specific temperature distribution in organs, due to an ablative device, is simulated. The effects of ablation are modeled. The modeling is patient specific. The vessel structure for a given patient, segmented from medical images, is accounted for as a heat sink in the model of biological heat transfer. A temperature map is generated to show the effects of ablation in a pre-operative analysis. Temperature maps resulting from different ablation currents and ablation device positions may be used to determine a more optimal location of the ablative device for a given patient. Other models may be included, such as accounting for the tissue damage during the ablation.