The effectiveness of 1, 6, 12, 24, 36 and 48 hours of continuous ambulatory electrocardiographic examination in detecting maximal ventricular ectopy was studied in 67 patients with coronary heart disease (45 with myocardial infarction, 22 with angina pectoris) and 23 normal subjects. Two consecutive 24 hour Holter recording examinations provided 48 hours of continuous examination. Ventricular ectopy was detected in 87 percent of patients and 35 percent of normal subjects. Complex forms (multifocal or repetitive patterns) were found in 62 percent and high frequency ectopy (greater than 60/hour) in 30 percent of the patients with coronary heart disease. Examination of either the initial hour of study or an hour of dynamic activity frequently failed to reveal the maximal ventricular ectopy present, particularly with regard to complex types and high frequency. Continuous 6 and 12 hour examinations were less effective than the 24 hour examination, which detected the maximal grade of ventricular ectopy in 71 to 74 percent and the maximal frequency in 58 to 83 percent of patients with coronary heart disease. Detection of maximal complex types and high frequency of ventricular ectopy was one to three times greater with a continuous 24 hour examination than with studies of shorter duration. Patient-recorded diaries showed that 50 to 80 percent of patients were engaged in mild to moderate activity during ventricular ectopy and only 9 percent indicated symptoms during the hours of maximal ventricular ectopy.