An apparatus and method for performing cardiac ablations employs a catheter comprising an anchoring device and an ablating device to perform the ablations to electrically isolate the pulmonary veins and left atrium from surrounding atrial tissue. The anchor can comprise a balloon-type device, a stent-like device, a strut-like device, a spring-strut-like device, an umbrella-like device, a mushroom-like device, or other device that allows the catheter to maintain a position with respect to target tissue. The ablator can comprise a balloon ablator, an umbrella ablator, a pinwheel ablator, an umbrella ablator incorporating a cinch mechanism, a mushroom balloon ablator and a segmented balloon or pinwheel ablator. The anchor and ablator can also comprise a combination mushroom balloon anchor section and mushroom balloon ablator section. The anchor and ablator can include electrodes for measuring a conductance therebetween when in deployed position, so as to determine the effectiveness of the ablation.