Annual deaths from tornadoes, earthquakes and floods together total fewer than 200. The most deadly heat wave in recent years occurred in Chicago over a week in July 1995, when temperatures hovered around 100 degrees.
Cardiac Cycle: 1st Systole Phase. During the systole phase, the right ventricle receives impulses from the Purkinje fibers and contracts. The atrioventricular valves close and the semilunar valves open. The de-oxygenated blood is pumped into the pulmonary artery.
The extrasystole is followed by a pause, as the heart electrical system resets itself and the contraction following the pause is usually more forceful than normal. These more forceful contractions are frequently perceived as palpitations. Systole refers to the time when the left ventricle of the heart contracts.