The statements list some of the events in the cardiac cycle. They are not in the correct order. Which statement describes the fifth of these events to occur in the cardiac cycle? 1 The impulse travels through Purkyne tissue. 2 A wave of excitation sweeps across the atria. 3 The atrioventricular node delays the impulse for a fraction of a second. 4 The sinoatrial node contracts. 5 The wave of excitation sweeps upwards from the base of the ventricles. 6 The ventricles contract. 7 The atria contract.