In regard to the first question, there is no doubt that yoga breathing exercises can influence frequency of heartbeat, force of cardiac contraction and intensity of heart sounds. (si.com)
The Horehound herb helps in improving the regularity of cardiac contraction in low doses, but a physician must be consulted before using it in this situation, and larger doses may cause abnormal heartbeat. (store.newwayherbs.com)
Exhaled air contains 17 percent oxygen, less than 21 percent of fresh air, and 4 percent carbon - dioxide, which can inhibit cardiac contraction. (uchospitals.edu)