Final answer:
Friedman and Rosenman found that individuals less likely to have a heart attack exhibited what they classified as Type B personalities, characterized by a relaxed and laid-back demeanor.
Step-by-step explanation:
Friedman and Rosenman's research into personality types in relation to heart disease led them to categorize individuals into Type A and Type B personalities. Type A individuals tend to be intensely driven and work-oriented, often experiencing high levels of stress. This personality type was linked, especially in earlier studies, to a higher incidence of heart disease. By contrast, those who are less prone to heart disease were identified as having a Type B behavior pattern, exhibiting more relaxed and laid-back attitudes. Therefore, the individuals who were less likely to have a heart attack according to Friedman and Rosenman are referred to as Type B personalities.