Polygenic inheritance can be explained as Mendelian inheritance at many loci, resulting in a trait which is normally-distributed. If n is the number of involved loci, then the coefficients of the binomial expansion of (a + b) 2n will give the frequency of distribution of all n allele combinations.
Once the pacemaker is implanted, the leads carry signals back from the heart. The pulse generator reads these signals and the batteries send electrical impulses to the heart to help pace it. Most pacemakers can sense the heart's rhythm and turn themselves off when the heartbeat is above a certain level. They will turn on again when the heartbeat is too slow. These types of pacemakers are called demand pacemakers.
People with pacemakers used to be told to steer clear of microwave ovens because of possible interference microwaves could cause to the electrical device implanted in their chests. Now they must worry about cell phones, security systems, magnetic resonance imaging (MRI), even therapeutic magnet mattress pads.