This study provides, for the first time, data that furnish an estimate of present and future manpower needs for cardiologists in the fields of patient care, teaching and research within the United States. The data collected provide a description of the current practice of cardiology and identify deficiencies in existing training programs in cardiology. Further, this study projects the future activities of cardiologists, and thus will aid in planning training and experience for them. The data collected should be of value to individuals, hospitals, universities, governmental agencies and voluntary health agencies that are concerned with providing administrative, financial and educational support for training programs in cardiology and that require cardiologists for patient care, teaching and research activities.