A method and apparatus for sensing in vivo blood pressure proportional to the left ventricular pressure for detecting ventricular tachyarrhythmias or the cardiovascular status in congestive heart failure, and/or for adjusting the rate of a pacemaker. A lead with a pressure sensor near its distal end is placed transvenously through the coronary sinus and located in the coronary vein. When in place, a bulge or an inflatable balloon proximal to the pressure sensor may be used to acutely occlude the coronary vein until the sensor fibroses in. The balloon may be reinflated prior to pressure measurements. The pressure that is sensed in that location is proportional to the left ventricular pressure. Values representing the left ventricular pulse, systolic and diastolic pressures, as well as the differentiated rate of change (i.e., dP/dt), gross rate of change (.DELTA.P/.DELTA.t) and mean or average of such pressure values are all or selectively developed by software algorithms and implemented in microprocessor based control circuitry. In one preferred embodiment, one or more of the values are utilized in software implemented algorithms to cause a pacemaker to pace the heart at a required rate to achieve a desired cardiac output. Alternatively, these left ventricular pressure related values may be employed to confirm the absence of mechanical pumping action of the heart which, in conjunction with other cardiac signals, confirm the existence of a tachyarrhythmia requiring anti-tachy pacing, cardioversion or defibrillation.