An ambulatory ventricular function anaylzer system is provided. The ambulatory ventricular function analyzer system is carried by a garment worn by a cardiac patient and includes ECG electrodes, a main left ventricular probe detector, and a background lung probe detector for providing diagnostically useful information while the patient goes about the normal activities of daily life. An information processing sub-system including a microprocessor responds to the electrode signal and to the probe signals and provides composite data representative of the ECG activity, the background lung time-activity, the left ventricular time-activity, and an R-wave histogram averaged over multiple cardiac cycles. The averaged data is sequentially sotred over a long time interval on magnetic tape in plural categories representing premature ventricular contraction, postpremature ventricular contraction, and normal ventricular contraction for subsequent display on a computer-based graphics display for study by a cardiac specialist. The main left ventricular function probe detector includes an array of cadmium telluride crystals mounted in a Pb housing having a parallel hole Pb collimator. The detector is substantially insensitive to position changes that arise during ambulatory monitoring.