摘要： The collection of long-term health data is accelerating with the advent of portable/wearable medical devices including electrocardiograms (ECGs). This large corpus of data presents great opportunities to improve the quality of cardiac care. However, analyzing the data from these sensors is a challenge; the relevant information from ～120 000 heart beats per patient per day must be condensed into a human-readable form. Our goal is to facilitate the analysis of these unwieldy data sets. We have developed an open source tool for creating easy-to-interpret plots of cardiac information over long periods. We call these plots ECG clocks. The utility of our ECG clock library is demonstrated through multiple examples drawn from a database of 24-h Holter recordings. In these case studies, we focus on the visualization of heart rate and QT dynamics. The ECG clock concept is shown to be relevant for both physicians and researchers, for identifying healthy and abnormal values and patterns in ECG recordings. In this paper, we describe how to use the ECG clock library to analyze 24-h ECG recordings, and how to extend the source code for your own purposes. The tool is applicable to a wide range of cardiac monitoring tasks, such as heart rate variability or ST elevation. This library, which we have made freely available, can help provide new insights into circadian patterns of cardiac function in individuals and groups.