Regarding cardiology and conduction characteristics- Tissue stimulation without direct effect (such as causing contraction in another chamber), but leading to a change in conduction characteristics. A common example would be an interpolated PVC (a type of premature ventricular contraction) during normal sinus rhythm; the PVC does not cause an atrial contraction, because the retrograde impulse from the PVC does not completely penetrate the AV node. However, this AV node stimulation (which is not visible on EKG by itself, hence "concealed") can cause a delay in subsequent AV conduction by modifying the AV node's subsequent conduction characteristics. Hence, the P-R interval after the PVC is longer than the baseline P-R interval.