Obstruction to blood flow, as occurs in valvular stenosis, can cause symptoms resembling those of myocardial failure (Chap. 252). Cardiac arrhythmias often develop suddenly, and the resulting symptoms and signs—palpitations (Chap. 39), dyspnea, hypotension, and syncope (Chap. 18)—generally occur abruptly and may disappear as rapidly as they develop.