Read the following passages carefully and answer the questions that follow. As heart disease continues to be the number one killer in the United States, researchers have become increasingly interested in identifying the potential risk factors that trigger heart attacks. High-fat diets and life in the fast lane have long been known to contribute to the high incidence of heart failure. But according to new studies, the list of risk factors may be significantly longer and quite surprising. Heart failure, e.g. appears to have seasonal and temporal patterns. A higher percentage of heart attacks occurs in cold weather and more people experience heart failure on Monday than on any other day of the week. In addition, people are more susceptible to heart attacks in the first few hours after waking. Cardiologists first observed this morning phenomenon in the mid-1980 and have since discovered a number of possible causes. An early morning rise in blood pressure, heart rate and concentration of heart stimulating hormones, plus a reduction of blood flow to the heart, may all contribute to the higher incidence of heart attacks between the hours of 8:00 am and 10:00 am. In other studies, both birthday and bachelorhood have been implicated as risk factors. Statistics reveal that heart attack rate increases significantly for both females and males in the few days immediately preceding and following their birthdays. And unmarried men are more at risk for heart attacks than their married counterparts. Though stress is thought to be linked in some way to all of the aforementioned risk factors, intense research continues in the hope of future comprehending why and how heart failure is triggered. Choose the word opposite in meaning to the word 'intense' as used in the passage.