A system for creating permanent lesions in target tissue proximate a junction between a pulmonary vein and a left atrium, the system comprising: a medical device including: an occlusion element coupled to a distal end of the medical device; a first temperature sensor coupled to the distal end of the medical device and located distal of the occlusion element; a second temperature sensor coupled to the distal end of the medical device and located proximal of the occlusion element; and a console including: a coolant source in fluid communication with the occlusion element; and a computer programmable to execute an algorithm for: comparing a first plurality of temperature measurements recorded by the first temperature sensor to a second plurality of temperature measurements recorded by the second temperature sensor to determine whether the occlusion element is occluding a pulmonary vein ostium; characterized in that a third temperature sensor is located within the occlusion element and the computer algorithm is also comparing the first plurality of temperature measurements to a set of reference temperatures that correlate blood temperature to tissue temperature to provide a temperature within the target tissue. a medical device including: an occlusion element coupled to a distal end of the medical device; a first temperature sensor coupled to the distal end of the medical device and located distal of the occlusion element; a second temperature sensor coupled to the distal end of the medical device and located proximal of the occlusion element; and a console including: a coolant source in fluid communication with the occlusion element; and a computer programmable to execute an algorithm for: comparing a first plurality of temperature measurements recorded by the first temperature sensor to a second plurality of temperature measurements recorded by the second temperature sensor to determine whether the occlusion element is occluding a pulmonary vein ostium; characterized in that a third temperature sensor is located within the occlusion element and the computer algorithm is also comparing the first plurality of temperature measurements to a set of reference temperatures that correlate blood temperature to tissue temperature to provide a temperature within the target tissue. a coolant source in fluid communication with the occlusion element; and a computer programmable to execute an algorithm for: comparing a first plurality of temperature measurements recorded by the first temperature sensor to a second plurality of temperature measurements recorded by the second temperature sensor to determine whether the occlusion element is occluding a pulmonary vein ostium; characterized in that a third temperature sensor is located within the occlusion element and the computer algorithm is also comparing the first plurality of temperature measurements to a set of reference temperatures that correlate blood temperature to tissue temperature to provide a temperature within the target tissue. comparing a first plurality of temperature measurements recorded by the first temperature sensor to a second plurality of temperature measurements recorded by the second temperature sensor to determine whether the occlusion element is occluding a pulmonary vein ostium; characterized in that a third temperature sensor is located within the occlusion element and the computer algorithm is also comparing the first plurality of temperature measurements to a set of reference temperatures that correlate blood temperature to tissue temperature to provide a temperature within the target tissue.