We can't make any kind of specific guess regarding your situation without having previous knowledge about your cardiovascular system and health. We really would hate to give you any kind of information that could be potentially harmful. Basically, both of these substances put strain on your heart. To what extent this combination will strain your heart, it's hard to tell.
Both of these substances are inherently strenuous on your heart. It's your decision whether you want to take this risk. As far as specifics, "will it kill me/won't it; will it cause damage/won't it", that's not possible. One thing I can definitely say, is that taking Caffeine while using Amphetamines makes you more likely to experience palpitations, anxiety and such. You really should focus more on how the Methamphetamine is affecting you and your health instead of the Caffeine.
Caffeine; Amphetamines, both strenuous on the Cardiovascular system, case closed.