Cardiac electrical and mechanical activity are closely interrelated not only via the chain of events, commonly referred to as “excitation–contraction coupling” (ECC), that links electrical excitation to contraction, but equally via feedback from the heart’s mechanical environment to the origin and spread of cardiac excitation. The latter has been termed mechano-electric feedback (MEF) and complements ECC to form an intracardiac electro-mechanical regulatory loop. This chapter will review MEF effects on heart rate (HR, number of beats per unit time, usually 1 min) and rhythm (regularity of cardiac contractions), distinguishing between pro- and anti-arrhythmic effects, and elucidate the extent to which stretch-activated ion channels (SAC) may explain observed responses. A concluding section addresses current shortfalls in insight and presents theories regarding the physiological relevance of MEF in the heart.