After reading this chapter you should be able to:

sketch the anatomy of the cardiac excitation–conduction system and state the role of each component (4.1);

explain ‘dominance’ (4.1) and the emergence of a slower pacemaker in heart block;

draw the sino-atrial node potential over one cardiac cycle and state the ionic basis of each phase (4.2);

explain how depolarization propagates through the myocardium (4.3);

state the chronotropic actions of (1) sympathetic and (2) parasympathetic nerves, and the underlying mechanisms (4.5; 4.6);

explain the inotropic and lusitropic effects of sympathetic stimulation (4.5);

describe the deleterious effect of hyperand hypokalaemia (4.8);

state the actions of (1) β-blockers and (2) Ca2+-channel blockers on the heart (4.9).