A respiration monitor for detecting effective respiration of a patient includes circuitry for suppressing the indication of unwanted signals due to heart activity, noise and flat breathing. A first threshold circuit is provided for increasing the sensitivity of the respiration monitor in response to a decreasing amplitude of the measured respiration signals. A first comparator circuit provides a fixed amplitude threshold below which detected signals are fully neglected. A second threshold circuit provides an adjustable amplitude threshold for the measured respiration signal, which threshold is raised in response to a decreasing respiration frequency below a predetermined frequency limit. Effective respiration is indicated only if all the aforementioned amplitude thresholds are exceeded.