A system for diagnosis or treatment of tissue in a body, comprising: an ablation catheter (20, 64, 74), comprising: a deformable, elongate shaft (52, 138, 160, 204, 244, 306, 370) having proximal and distal ends; a first ablation delivery member (58, 108, 136, 162) disposed proximate said distal end of said shaft (52, 138, 160, 204, 244, 306, 370), said first ablation delivery member (58, 108, 136, 162) configured to deliver ablation energy to ablate said tissue, said first ablation delivery member (58, 108, 136, 162) disposed about a longitudinal axis of said shaft (52, 138, 160, 204, 244, 306, 370) and having proximal and distal ends, said first ablation delivery member (58, 108, 136, 162) configured to bend relative to said longitudinal axis between said proximal and distal ends of said first ablation delivery member (58, 108, 136, 162), wherein said first ablation delivery member (58, 108, 136, 162) includes a sidewall having a plurality of elongated slits extending therethrough; a lumen (82, 84, 170, 224) located within the ablation delivery member (58, 108, 136, 162), the lumen (82, 84, 170, 224) adapted to deliver fluid configured to control the temperature of the first ablation delivery member (58, 108, 136, 162); a return lumen (186, 226) configured to draw the fluid away from the first ablation delivery member (58, 108, 136, 162); a membrane positioned over the plurality of elongate slits and over at least a portion of an exterior surface of the ablation delivery member, the membrane configured to prevent the fluid from flowing out of the ablation delivery member to provide a closed-loop pathway between the lumen and the return lumen; a first sensing electrode disposed proximate said first ablation delivery member (58, 108, 136, 162), said first sensing electrode configured to generate a first signal indicative of electrical activity in said tissue; a force sensing element (134, 144, 168, 200, 212, 254, 256, 300, 302, 316, 318, 364, 366, 380, 382, 428, 430) coupled to the first ablation delivery member (58, 108, 136, 162) and configured to detect a force applied to the first ablation delivery member (58, 108, 136, 162); and an electronic control unit (26, 166, 210, 252, 314, 378) configured to control delivery of said ablation energy from said first ablation delivery member (58, 108, 136, 162) responsive to said first signal and to determine a degree of coupling between said first ablation delivery member (58, 108, 136, 162) and said tissue based on the detected force. a deformable, elongate shaft (52, 138, 160, 204, 244, 306, 370) having proximal and distal ends; a first ablation delivery member (58, 108, 136, 162) disposed proximate said distal end of said shaft (52, 138, 160, 204, 244, 306, 370), said first ablation delivery member (58, 108, 136, 162) configured to deliver ablation energy to ablate said tissue, said first ablation delivery member (58, 108, 136, 162) disposed about a longitudinal axis of said shaft (52, 138, 160, 204, 244, 306, 370) and having proximal and distal ends, said first ablation delivery member (58, 108, 136, 162) configured to bend relative to said longitudinal axis between said proximal and distal ends of said first ablation delivery member (58, 108, 136, 162), wherein said first ablation delivery member (58, 108, 136, 162) includes a sidewall having a plurality of elongated slits extending therethrough; a lumen (82, 84, 170, 224) located within the ablation delivery member (58, 108, 136, 162), the lumen (82, 84, 170, 224) adapted to deliver fluid configured to control the temperature of the first ablation delivery member (58, 108, 136, 162); a return lumen (186, 226) configured to draw the fluid away from the first ablation delivery member (58, 108, 136, 162); a membrane positioned over the plurality of elongate slits and over at least a portion of an exterior surface of the ablation delivery member, the membrane configured to prevent the fluid from flowing out of the ablation delivery member to provide a closed-loop pathway between the lumen and the return lumen; a first sensing electrode disposed proximate said first ablation delivery member (58, 108, 136, 162), said first sensing electrode configured to generate a first signal indicative of electrical activity in said tissue; a force sensing element (134, 144, 168, 200, 212, 254, 256, 300, 302, 316, 318, 364, 366, 380, 382, 428, 430) coupled to the first ablation delivery member (58, 108, 136, 162) and configured to detect a force applied to the first ablation delivery member (58, 108, 136, 162); and an electronic control unit (26, 166, 210, 252, 314, 378) configured to control delivery of said ablation energy from said first ablation delivery member (58, 108, 136, 162) responsive to said first signal and to determine a degree of coupling between said first ablation delivery member (58, 108, 136, 162) and said tissue based on the detected force.