The title suggests a medical setting, but the poem treats the heart as something closer to a moral or emotional possession. The speaker begins by saying his heart was so good, and he so happy, that he felt jealous of himself. It is a funny, slightly dizzying idea: envying the person you used to be, or the person you could be on a good day.
Then the tone turns. The speaker says he "serves" his heart in a sandwich, an odd, almost darkly comic image that suggests he has cheapened or consumed what was best in him. He is now "quite another man," which reads as a loss of self. The last lines reach for cures: holy water to drink, and spare change that turns his heart into moonshine. Judging by the imagery, he is mixing the sacred with the intoxicating, hoping for healing but drifting toward something dizzy and unreliable. The mood is wry, uneasy, and quietly sad.