A simple device for measuring the momentary cardiac frequency (i.e. a value proportional t-r the length of the time interval between two cardiac contractions) is worked out using a capacitoo transducer consisting of two capacitors and an electron control circuit. The sequence of the charging, indication of the voltage and the discharge of the capacitors is effected by a relay circuit. A random signal characterizing the cardiac cycle can be used as input signal, such as: ECG, pulse signal, signal of the blood pressure transducer, etc. At a definite moment of the cardiac cycle the device produces a synchroimpulse. This makes it possible, by regulating the delay between the triggering and the stimulating impulses of an external stimulator, to realize a regime of synchronized stimulation, i.e., the stimulating impulses to coincide with a preliminarily given moment after the beginning of the cardiac cycle. The output of the device is connected with a standard recording device with sufficiently large input resistance. The transistor electronic circuit is connected to the supply or to an autonomous source. The dimensions of the device are 20 X 12 X 10 cm, its weight is about 2 kg.