Figure 1 Representative relation of QT interval to heart rate (HR) during 24 hour Holter ECG recordings from a 50 year old healthy man. Number of data points was 5701 and correlation coefficient (r²) was 0.57. The dotted lines indicate the upper and lower limits of the normal QT interval (mean (2SD)) obtained from the nomogram (table 2). Almost all data points fell into the normal range.