A method for sensing multiple local electric voltages from endocardial surface of a heart, includes: providing a system for sensing multiple local electric voltages from endocardial surface of a heart, including: a first elongate tubular member having a lumen, a proximal end and a distal end； a basket assembly including: a plurality of flexible splines for guiding a plurality of exposed electrodes, the splines having proximal portions, distal portions and medial portions therein between, wherein the electrodes are substantially flat electrodes and are substantially unidirectionally oriented towards a direction outside of the basket.
