A device comprising: two or more electrodes (800, 802, 804, 806, 808, 810); a sensing circuit coupled to the two or more electrodes (800, 802, 804, 806, 808, 810) and configured to obtain a signal indicative of electrical activity of a patient's heart; and a processor or controller configured to: detect R-waves based on comparisons of the signal indicative of electrical activity of the patient's heart, or samples thereof, to an R-wave detection threshold; and determine whether an R-wave detection should be classified as a false R-wave detection due to T-wave oversensing or P-wave oversensing by: comparing a specific morphological characteristic associated with the R-wave detection to the specific morphological characteristic associated with each R-wave detection in a first set of earlier detected R-wave detections that includes R-wave detection that were one, two, and three R-wave detections earlier to thereby determine whether first TWO or PWO morphological criteria are met, and in a second set of earlier detected R-wave detections that includes R-wave detections that were two, three, and four R-wave detections earlier to thereby determine whether second TWO or PWO morphological criteria are met, wherein the second set differs from the first set but may have some overlap with the first set; and classifying the R-wave detection as a false R-wave detection in response to one of the first or second TWO or PWO morphological criteria being met. two or more electrodes (800, 802, 804, 806, 808, 810); a sensing circuit coupled to the two or more electrodes (800, 802, 804, 806, 808, 810) and configured to obtain a signal indicative of electrical activity of a patient's heart; and a processor or controller configured to: detect R-waves based on comparisons of the signal indicative of electrical activity of the patient's heart, or samples thereof, to an R-wave detection threshold; and determine whether an R-wave detection should be classified as a false R-wave detection due to T-wave oversensing or P-wave oversensing by: comparing a specific morphological characteristic associated with the R-wave detection to the specific morphological characteristic associated with each R-wave detection in a first set of earlier detected R-wave detections that includes R-wave detection that were one, two, and three R-wave detections earlier to thereby determine whether first TWO or PWO morphological criteria are met, and in a second set of earlier detected R-wave detections that includes R-wave detections that were two, three, and four R-wave detections earlier to thereby determine whether second TWO or PWO morphological criteria are met, wherein the second set differs from the first set but may have some overlap with the first set; and classifying the R-wave detection as a false R-wave detection in response to one of the first or second TWO or PWO morphological criteria being met. detect R-waves based on comparisons of the signal indicative of electrical activity of the patient's heart, or samples thereof, to an R-wave detection threshold; and determine whether an R-wave detection should be classified as a false R-wave detection due to T-wave oversensing or P-wave oversensing by: comparing a specific morphological characteristic associated with the R-wave detection to the specific morphological characteristic associated with each R-wave detection in a first set of earlier detected R-wave detections that includes R-wave detection that were one, two, and three R-wave detections earlier to thereby determine whether first TWO or PWO morphological criteria are met, and in a second set of earlier detected R-wave detections that includes R-wave detections that were two, three, and four R-wave detections earlier to thereby determine whether second TWO or PWO morphological criteria are met, wherein the second set differs from the first set but may have some overlap with the first set; and classifying the R-wave detection as a false R-wave detection in response to one of the first or second TWO or PWO morphological criteria being met. comparing a specific morphological characteristic associated with the R-wave detection to the specific morphological characteristic associated with each R-wave detection in a first set of earlier detected R-wave detections that includes R-wave detection that were one, two, and three R-wave detections earlier to thereby determine whether first TWO or PWO morphological criteria are met, and in a second set of earlier detected R-wave detections that includes R-wave detections that were two, three, and four R-wave detections earlier to thereby determine whether second TWO or PWO morphological criteria are met, wherein the second set differs from the first set but may have some overlap with the first set; and classifying the R-wave detection as a false R-wave detection in response to one of the first or second TWO or PWO morphological criteria being met.