The 8th house of the ascendant (Lagna) chart is known as the house of longevity, or perhaps even the house of death (Mrityu Bhava). Like the 6th and 12th houses, it is a malefic house where no benefic planet does well; in fact, even malefic planets like Rahu in the 8th house turn into killers which can cause considerable distress to the native, perhaps even death.
The only known planets that can somewhat still give benefic results in the 8th house would be Jupiter and the Sun – and that too when or if they are posited in their own signs (Pisces and Sagittarius for Jupiter, and Leo for the Sun) or in exaltation (Cancer for Jupiter, Aries for the Sun). In other cases, their benefic effects too are considerably affected.
Now, Venus in the 8th house of the Lagna chart or ascendant chart is a topic for special discussion.
From my personal experience, unless Venus is exalted in the 8th house, which happens for Leo ascendants, or in its own signs, which are Libra and Taurus, it is NOT a good placement.
And even in those zodiac signs, with the exception of Pisces, Venus will only give longevity or age to the person and some wealth; however, they will still be facing some kind of loss.
The situation gets worse for ascendants who do not have a zodiac sign that is favorable for Venus in the 8th house.
For example, Venus in the 8th house for a Virgo ascendant will be in Aries. Now, the problem is that Venus is a great benefic, but it performs poorly in the 8th house if it is placed in Aries, which is a zodiac sign owned by Mars.
Now, if Mars, who is the lord of the 8th house is debilitated, then the entire 8th house will begin affecting Venus. For example, if Mars is in the 11th house in Cancer, where it is debilitated, then the native will end up having relationships or emotional heartbreaks one after another – this is because Venus is the planet of love, relationships, passion, sex, etc. However, for Virgo ascendants, it becomes a Marak Grah (killer planet). Furthermore, if the Moon is also badly placed in the native’s chart, such as in the 6th house or perhaps in conjunction with a malefic planet like Saturn (Moon Saturn conjunction creates Vish Dosh which is a highly inauspicious phenomenon known for causing lifelong stress and emotional pain to the native) then the person will likely end their lives due to being hurt in relationships or in love. As previously mentioned in another post, malefic planets become three times more damaging when retrograde. However, a retrograde debilitated planet will give surprisingly good results to the native, more so when it is malefic.
*Reference – in any ascendant chart, the lord or ruling planet of the zodiac signs inhabiting the 2nd and the 7th house are known as killer planets or Marak Grah. If a Marak Grah ends up occupying the 8th house, which is known as the Mrityu Bhava or the house of death, its ability to kill the native increases rapidly. Among benefic planets, Venus is the most powerful killer planet, while in malefics, Saturn is the most powerful killer planet. In any chart, if those two or either of the planets being Marak Graha are posited in the 8th house, they will eventually kill the native in their respective ways. For Capricorn and Aquarius ascendants, Rahu in the 8th house becomes a strong Marak Grah; in other cases, He will continue to cause distress depends on the condition of the 8th house which may or may not result in the death of the native, though it depends on the condition of Jupiter in the chart as well.
As such, a poorly placed Venus in the 8th house will also cause considerable financial losses to the native because Venus would be looking at the 2nd house of the ascendant chart through His 7th aspect, and the 2nd house governs income, bank balance, wealth, etc.
If Venus is NOT the lord of the 2nd and/or the 7th house of the ascendant chart and is posited in a friendly sign in the 8th house, He will give the person an increased lifespan and longevity. However, Venus in the 8th house will also increase the chances of the person attempting to find happiness and emotional fulfillment or sexual consummation in hidden relationships or secret affairs.
If Venus is aspected by a benefic, its ability to give a decent life to the native increases; however, wealth loss will still happen unless it is in exaltation or in its own sign.