Eighty-three children were monitored by Holter electrocardiography for ventricular premature contraction (VPC), and the relationship between the preceding RR interval and the coupling interval was plotted using a two-dimensional RR interval plotting method. With this method, the slope (a) and standard deviation (SD) of the linear regression (Y = aX+b) were determined. These parameters were used to classify the patients into one of two types: a fixed type (SD < 40 msec, a < 0.2) and an unfixed type. The unfixed type was further divided into four subtypes, based on the plotted morphology: scattered, dependent, biphasic, and intermediate. The relationships between the VPC origin, organic heart disease, ventricular tachycardia (VT) and parasystole were investigated in the five types. The fixed and dependent types comprised significantly greater proportions of the subjects with VPC of right ventricular origin than of subjects with VPC of left ventricular origin (fixed: 31/59 right VPC vs 4/24 left VPC, p < 0.005; dependent: 13/59 vs 1/24, p < 0.05). On the other hand, comparatively very few subjects of the scattered type showed right VPC (4/59 vs 18/24, p < 0.005). Finally, the biphasic and intermediate types were distributed fairly equally among the subjects with VPCs of right and left ventricular origin (biphasic: 5/59 vs 0/24, p = 0.31, intermediate: 6/59 vs 1/24, p = 0.67). Organic heart disease was present in 13 subjects (15.7% of total subjects), seven of whom were of the fixed type with right ventricular origin (22.6% of subjects of this type). VT was observed in 34 subjects, but was rare in the scattered type (2/22 subject, 9.1%).(ABSTRACT TRUNCATED AT 250 WORDS)