Final answer:
The pacemaker cells are specialized conducting cells in the heart that send electrical signals for it to contract, initiating the heart's rhythm via the cardiac conduction system.
Step-by-step explanation:
The group of cells that send electric signals to contract the heart is called the pacemaker cells. These specialized myocardial conducting cells have the unique ability to trigger action potentials automatically, a feature known as autorhythmicity. The pacemaker cells, primarily located at the sinoatrial (SA) node, start the cardiac conduction system. They are responsible for setting the heart's rhythm by spontaneously generating electrical impulses at regular intervals. These impulses spread through the heart's conduction system, which includes the SA node, atrioventricular (AV) node, bundle of His, bundle branches, and Purkinje fibers, to ensure that the heart contracts efficiently as a functional unit.