A heat pad for pressing against a curved surface of an annular tire to vulcanize a tire patch having a channel-shaped sheet member of resilient conductive rubber material with reinforcing electrodes adhered to the sheet member at the elongated side edges, a cover of insulating rubber material encasing the sheet member and an intermediate portion between the electrodes stretchable to conform to the curved surface of the tire under pressure from a pressing member urging the pad against the tire.