Heart

Major signs of healthy heart include:

1. Loving Allah (SWT) more than anything or anyone else. In Quran (And the believers love Allah more )(2: 165). Loving Allah (SWT) makes the believer love what Allah wants and keep away from what Allah dislikes.

2. Feeling the taste of talking to Allah in Prayers and supplications as well as the taste of listening to Allah in reciting or listening to Quran. Nothing more tasteful than talking to the Most beloved and listening to His Words.

3. Enjoying performing the Prayers because it is a direct contact with Allah (SWT). Beside the obligatory Prayers, performing the recommended Prayers like Nawaafil and Night Prayers is a sign of healthy heart.

4. Loving Allah's most beloved ones who are the prophets and Infallible Imams, more than loving ourselves and our families. 

5. Loving all the creatures of Allah and feeling sympathy to them except the enemies of Allah (SWT).

Wassalam.

Dead heart does affect your intellect because it affects your soul and brain and way of thinking and your lifestyle. Dead heart disturbs the whole life in every dimension, that is why it is crucial to do everything possible to clarify the heart and remove the blots of sinful acts from it by repeating Estighfaar and performing the obligatory duties and avoiding the sins.

Wassalam.

Repeated sins with out seeking forgiveness cause seal on the heart. Every sinful act causes a blot on the heart which can be removed by sincerely seeking forgiveness. When the sinful deeds are repeated, the black blots cover the heart and seal it. The person with sealed heart does not feel the taste of Prayers or Du'a or Quran etc. Sealed heart is like a dead heart.

Removing the seal from the heart is always possible if the person is really willing  and ready to act to remove the seal. It starts with sincere repentance and seeking forgiveness and establishing a firm decision not to commit the sins again.

Repeating Estighfaar, with deep feeling of sorrow for committing the sinful acts, is very important in this regard.

Returning back the rights to the victims is also very important.

Performing all Prayers on time as well as reciting  Quran, Du'a, Ziyarat Ashura, Night Prayer is very helpful.

Wassalam.

The difference between the heart قلب and the breast or chests صدور in Quran has been discussed by many scholars of Tafseer. We see some non Shia scholars claim that there is no difference between heart and breast. We can not accept this opinion because of the clear mention of hearts and breasts in the same Quranic verses which must mean a difference in the meanings.

Among many opinions, we can say that the breast or chest is wider than the heart and it is effected by the state of mind and feeling of comfort or discomfort. That is why we read the supplication of prophet Moses (AS): O my Lord, extend my breast (Taha: 25).

The heart is our inner which is the origin of our intentions, while the breast is effected also by outside reasons and factors which make us feel comfortable or otherwise. That is why we read in Sura Al-Inshiraah how Allah (SWT) tells His Prophet Muhammad (SAWA) mentioning His bounties on him: Did not We extend your breast? ألم نشرح لك صدرك which means that Allah (SWT) Has granted him this bounty of making his breast big and extended.

In Quran we read about Quran that it is : Cure for what is in the breasts وشفاء لما في الصدور (Younus : 57). What is in breasts can be a mixture of our feelings and our thinking and reactions to other factors surrounding us. 

No doubt, heart is the Centre of the breast (Hearts inside the breasts) (ولكن تعمى القلوب التي في الصدور) )(Verily, it is not the eyes that grow blind, but it is the hearts which are inside the breasts that grow blind) Al-Hajj : 46.

Wassalam