There is disclosed an electrocardiographic review system for displaying ECG data for each of eight patients. Whenever the data for a new patient is to be observed, two trend plots are first displayed on the screen. One of these represents the number of heartbeats per minute and the other represents the number of ectopic beats per minute, the time axis being divided into approximately 240 discrete 1-minute intervals so that the trend date for a 4-hour monitoring period can be displayed. The reviewing physician can move a cursor across the screen to a point of particular interest, for example, to a point along the time axis corresponding to a 1-minute interval during which many ectopic beats were detected. Following this, when a display key in the system is operated, a 4-second stationary display of the first ECG waveform of interest which occurred during that 1minute interval is formed. Thereafter, each operation of the display key controls the display of another 4-second ECG waveform. In this manner, the reviewing physician can determine those intervals during monitoring which are of particular interest, and can then immediately control the display of the successive 4-second ECG waveforms on the screen. The same screen is thus used to display both compressed-time trend data, and expanded-time ECG waveforms.