Is it permissible or forbidden for a single person living in Germany, who is unable to marry and suffers from heart pain, to engage in sexual activity, given that doctors have advised him to do so, even though all his medical tests are good?

Whoever advised you to seek healing through unlawful sexual practices did not give you good counsel, but rather deceived you. Allah has not placed the healing of the Ummah in committing unlawful acts; such acts are a disease, not a cure. Indeed, Ibn Mas'ud (may Allah be pleased with him) said: "Verily, Allah has not placed your healing in that which He has forbidden to you." The questioner should seek a trustworthy doctor, turn to Allah with supplication, asking Him for healing, and be diligent in performing ruqyah (definition) (Islamic exorcism/incantation) upon himself, or have a righteous person perform it for him.

We also advise you to hasten to marry if possible, for there is much good in it. Marriage is one of the causes of richness and a means by which Allah aids the one who marries seeking chastity. Allah may also make marriage a cause for your healing.