This case is about a community-based participatory research project called HEART that addressed prevention of heart disease and involved community health workers. Community health workers are members of the community who work as frontline public health workers. Community health workers connect people with providers and services, provide education, promote policies that affect the community, and fulfill many other roles. The project took place over 8 years in a large city along the U.S.–Mexico border and consisted of two parts. The first part tested whether participants who received an educational curriculum taught by community health workers improved cardiovascular health compared with a group who just received the materials. Both groups improved, with slightly greater changes among the group taught by community health workers. The second study aimed to increase use of existing facilities in participants' neighborhoods and provided free Young Women's Christian Association (YWCA) memberships. Community health workers also organized many different exercise and nutrition classes held at the Young Women's Christian Association and parks and recreation centers. People attended a high number of sessions, improved their physical activity and diet, and reduced their weight and waist circumference, although one-third of participants did not complete the follow-up assessments. Many lessons were learned from the project, including the need for and difficulty of balancing scientific rigor with community needs. It is essential to have input from community members about these decisions at every step of the way. Decisions on research design, data collection and management, and dissemination all affect both the strength of the research and the potential for real-world impact.